All topics

Every topic in the atlas, in alphabetical order. 334 topics.

A

Abstraction Hiding complexity behind a simpler interface — the core technique that lets us build and reason about large systems by ignoring lower-level details until we need them. Foundations
Accessibility Designing software that people with diverse abilities — visual, auditory, motor, cognitive — can use effectively. Human-Computer Interaction
ACID Transactions A transaction model that guarantees Atomicity, Consistency, Isolation, and Durability — the contract that keeps databases reliable under failures and concurrency. Data and Databases
Actor Model A concurrency model where independent actors communicate only through message passing — no shared memory, no locks — making it natural for fault-tolerant, distributed, and highly-concurrent systems. Distributed Systems and Cloud
Ada Lovelace 19th-century mathematician (1815–1852) who wrote the first algorithm intended for a machine — Charles Babbage's Analytical Engine. History and Society
Agile A family of iterative software development practices emphasising short cycles, working software, and adapting to change over upfront planning. Software Engineering
Alan Turing British mathematician and logician (1912–1954) whose 1936 paper laid the foundations of theoretical computer science. History and Society
Algorithms A precise, finite recipe for solving a problem — the central idea of computer science. Foundations
Anti-Aliasing A technique for reducing the "jaggies" (staircase effect) in digital images by smoothing the transition between foreground and background pixels — using spatial supersampling, temporal accumulation, or AI upscaling. Graphics and Media
Anycast Advertising the same IP address from multiple locations so BGP routes each user to the nearest one — the mechanism behind Cloudflare's global network, 1.1.1.1, and the DNS root servers. Networks and Internet
ARM vs x86 The two dominant CPU instruction set architectures — x86 (complex, high-performance, dominant in PCs and servers) and ARM (power-efficient, dominant in mobile and increasingly in servers and laptops) — with fundamentally different design philosophies converging in practice. Computer Architecture
ARPANET The Advanced Research Projects Agency Network (1969) — the first packet-switched computer network, connecting US university research sites, and the direct technological ancestor of the modern internet. History and Society
ASIC A chip designed for a single specific purpose — providing the maximum possible performance and power efficiency at the cost of inflexibility and multi-million dollar fabrication investment, used for Bitcoin mining, AI accelerators, and mobile SoCs. Hardware
Attention Mechanism A neural-network technique that lets a model weigh which parts of its input matter most for each part of its output — the key idea behind transformers and modern language models. Artificial Intelligence
Authentication Proving *who* a user is — by something they know (password), have (token, phone), or are (biometric). Security and Privacy
Authorization Deciding *what* an authenticated user is allowed to do — the system of permissions, roles, and policies that protects resources. Security and Privacy
Automata Abstract machines that read input and move between states according to fixed rules — the mathematical models of computation, from simple finite-state machines up to the Turing machine. Foundations

B

B-Tree A self-balancing tree optimised for block storage — wide, shallow, and designed so every search, insert, and delete touches only O(log n) pages, which is why it powers almost every database index. Foundations
Backpropagation The algorithm that computes how much each weight in a neural network contributed to the error — applying the chain rule layer by layer in reverse so gradient descent knows which way to adjust every parameter. Artificial Intelligence
Bayesian Inference Updating a belief about the world when new evidence arrives — Bayes' rule turned into a systematic method for learning from data while accounting for prior knowledge. Mathematical Foundations
BGP The routing protocol that holds the internet together — autonomous systems exchange reachability information so each router knows how to forward packets to any IP address on earth. Networks and Internet
Big O A notation for describing how an algorithm's cost grows as its input grows — the standard way computer scientists compare algorithms. Foundations
Binary Numbers A way of writing whole numbers using only two digits, 0 and 1 — the native number system of digital computers. Foundations
Bit A bit is the smallest unit of information in computing — a single value that is either 0 or 1. Foundations
Blue-Green Deployment A release strategy that runs two identical production environments — one live, one idle — and switches all traffic to the new version at once, so rollback is instant. Operations and Reliability
Boolean Logic The algebra of true and false — the simple rules (AND, OR, NOT) from which every digital decision is built. Foundations
Branch Prediction A CPU technique that guesses the outcome of a branch (an if or a loop) before it's actually known, so the pipeline can keep executing instead of stalling — and rolls back if the guess was wrong. Computer Architecture
Branchless Programming Replacing conditional branches with arithmetic and bit-manipulation so the CPU's branch predictor is never wrong — turning misprediction penalties into simple computation. Low-Latency Systems
Bus A set of wires (or differential lanes) that carries data, addresses, or control signals between components inside a computer. Hardware

C

C A compact, portable systems programming language designed in the early 1970s — the implementation language of Unix and, to this day, of most operating systems, compilers, and infrastructure. Programming Languages
Cache Small, fast memory close to the CPU that keeps recently or about-to-be-used data, hiding the slowness of main memory. Computer Architecture
Cache Coherence The set of protocols that keep multiple CPU caches in sync so all cores see a consistent view of memory. Computer Architecture
Cache-Line Alignment Laying data out to match the CPU's cache lines — so hot fields share a line, unrelated fields don't, and the processor stops wasting fetches and fighting over ownership. Low-Latency Systems
Calculus Basics The mathematics of change and accumulation — derivatives measure rates, integrals add them up. In computing it powers optimisation and the training of machine-learning models. Mathematical Foundations
Canary Deployment A release strategy that rolls a new version out to a small fraction of users first, watches its metrics, and gradually increases the share only if it's healthy — limiting the blast radius of a bad release. Operations and Reliability
CAP Theorem A foundational result of distributed systems: under a network partition, a system can be either Consistent or Available, not both. Distributed Systems and Cloud
Capability-Based Security A security model where authority to access a resource is represented by an unforgeable token (a capability) that must be explicitly held and passed — removing the need for centralised access control tables and preventing ambient authority vulnerabilities. Operating Systems
Category Theory An abstract mathematical framework studying structures and the structure-preserving maps between them — the algebraic language behind Haskell's monads, functional programming abstractions, and the compositional design of software. Foundations
CDN A global network of edge servers that caches and serves content close to users — making the web feel fast from anywhere on Earth. Networks and Internet
Certificate Authority A trusted organisation that issues digital certificates binding a public key to an identity — the root of trust that makes HTTPS and code signing trustworthy without pre-distributing keys. Security and Privacy
Chaos Engineering The practice of deliberately injecting failures into production systems to discover weaknesses before they cause unexpected outages — building confidence in a system's resilience by verifying it can withstand turbulent conditions. Operations and Reliability
Character Encoding The standard that maps characters to numbers so text can be stored and transmitted as bits — from ASCII's original 128 code points to Unicode's 150,000 and UTF-8's dominant variable-length encoding. Foundations
CI/CD An automated pipeline that builds, tests, and ships code on every change — so the path from "git push" to "in production" is short, repeatable, and safe. Software Engineering
Circuit Breaker A fault-tolerance pattern that stops calling a failing dependency and returns a fast error instead — giving the dependency time to recover and preventing cascading failures across services. Distributed Systems and Cloud
Clock The steady electronic pulse that synchronizes a digital circuit — every "tick" advances the CPU and other components through their next step, and its rate is measured in hertz. Hardware
Closure A function that captures variables from its enclosing scope — carrying its environment with it so it can access those variables even after the outer function has returned. Programming Languages
Cloud Provider A company that rents computing — servers, storage, networking, and managed services — on demand over the internet, so you don't have to build and run your own data center. Distributed Systems and Cloud
Code Review Reviewing someone else's proposed code change before it lands — the most reliable practice for catching bugs and spreading knowledge in teams. Software Engineering
Codec A pair of algorithms — encoder and decoder — that compress and decompress media. The reason a 4K video isn't a terabyte. Graphics and Media
Color Space A specific way of describing colours numerically — defining which RGB triplets (or other coordinates) mean which colours in the real world. Graphics and Media
Colour Management A system for ensuring that colours are reproduced consistently across different devices — cameras, monitors, and printers — by converting between device-specific colour spaces using ICC profiles and a device-independent colour reference space. Graphics and Media
Columnar Store A database that stores each column's values contiguously rather than each row — enabling far faster analytical queries that aggregate millions of rows but touch only a few columns. Data and Databases
Command-Line Interface A text-based user interface where you type commands and read text output — small, fast, scriptable, and the default for system administration and development. Human-Computer Interaction
Compiler A program that translates source code in one language into another — usually a high-level language into machine code or an intermediate form. Programming Languages
Complexity Theory The study of how the resources a problem requires — time and memory — grow with input size, and how problems are classified by how hard they are to solve. Foundations
Computability The study of what can be computed by an algorithm at all — and the proof that some problems, like the halting problem, can never be solved by any computer. Foundations
Computer Vision The field of teaching computers to interpret images and video — classification, detection, segmentation, generation. Artificial Intelligence
Consensus A protocol that lets a group of machines agree on a single value despite failures and network unreliability — the foundation under replicated databases and leader election. Distributed Systems and Cloud
Container A lightweight, isolated unit of computing — a process running with its own filesystem and namespaces, packaged with its dependencies. Distributed Systems and Cloud
Context Switch The act of saving one thread's CPU state and loading another's so the same CPU core can run a different thread next. Operating Systems
Continuation A representation of "the rest of the computation" as a first-class value — enabling full control over control flow, the basis for implementing coroutines, generators, exceptions, and async/await at the language level. Programming Languages
Convolutional Neural Network A neural-network architecture that uses convolution to detect local patterns — edges, textures, shapes — in grid-like data such as images; the workhorse of computer vision for a decade. Artificial Intelligence
Copy-on-Write A resource management optimisation where copying is deferred until modification — shared pages are kept as a single copy until one party writes, triggering a private copy only then. Operating Systems
Core Affinity Binding a thread permanently to a specific CPU core — eliminating migration overhead, warming the core's private caches, and making execution timing predictable. Low-Latency Systems
CPU The component of a computer that fetches and executes instructions — the place where programs actually run. Hardware
CPU Pipeline An assembly-line technique for executing instructions — split each instruction into stages and overlap many in flight at once. Computer Architecture
CRDT A data structure designed so that any two replicas can be merged in any order and still arrive at the same result — enabling eventual consistency without coordination. Distributed Systems and Cloud
Cryptography The science of keeping information secret and verifying it has not been tampered with — built from math and careful engineering. Security and Privacy
CSRF A vulnerability where an attacker tricks the victim's browser into making a state-changing request to a site the victim is logged into. Security and Privacy

D

Daemon A long-running background process with no controlling terminal, usually started at boot and supervised by the system, that quietly does work or waits for requests. Operating Systems
Dark Pattern User interface designs that trick, confuse, or coerce users into unintended actions — subscribing to services, sharing data, or making purchases they did not intend — through deliberate manipulation of attention and decision-making. Human-Computer Interaction
Data Structure A way of organising values in memory so that the operations you care about — find, insert, delete, sort — are efficient. Foundations
Data Warehouse A database optimized for analytics — large-scale querying and aggregation over historical data from across an organization — rather than for the fast small transactions of an operational database. Data and Databases
Data-Oriented Design Organising code around the memory layout data needs rather than object-oriented abstractions — transforming how systems are structured so the CPU spends time computing, not waiting for cache misses. Low-Latency Systems
Database An organised collection of data with a system around it that lets you store, retrieve, update, and query it efficiently. Data and Databases
Deadlock A state where two or more threads are each waiting for the other to release a lock — so none of them ever make progress. Operating Systems
Debugging The systematic process of finding and fixing the root cause of a software defect — using debuggers, logging, binary search, and reasoning from evidence to isolate incorrect behaviour. Software Engineering
Decision Tree A model that splits data by asking yes/no questions at each node, forming a tree of decisions that is transparent, interpretable, and the building block of powerful ensemble methods. Artificial Intelligence
Dennard Scaling The empirical rule that as transistors shrink, their power consumption decreases proportionally — allowing faster clock speeds at the same power budget. It broke down around 2004, ending the era of ever-faster single-core CPUs. Hardware
Dennis Ritchie The Bell Labs researcher who created the C programming language and co-created Unix — two inventions that together underpin almost all modern software. History and Society
Deployment The act of getting new versions of software running in production safely, predictably, and without downtime. Operations and Reliability
Design Pattern A named, reusable solution to a recurring design problem in code. A shared vocabulary that lets engineers describe structure without re-explaining it. Software Engineering
Design System A shared, documented set of reusable UI components, patterns, and guidelines that keeps a product's interface consistent and lets teams build faster. Human-Computer Interaction
DHCP The protocol that automatically assigns IP addresses, subnet masks, gateways, and DNS servers to devices when they join a network — the reason you don't manually configure an IP every time you connect to Wi-Fi. Networks and Internet
Diffusion Model A generative model that learns to remove noise from corrupted data, step by step — the approach behind Stable Diffusion, DALL-E, and Sora that produces startlingly realistic images and video. Artificial Intelligence
Discrete Mathematics The branch of mathematics dealing with distinct, separate values — logic, sets, combinatorics, graphs, and proof — that forms the mathematical foundation of computer science. Foundations
Distributed System A system whose components run on multiple networked computers and coordinate by passing messages. Distributed Systems and Cloud
DMA Direct Memory Access — hardware that lets devices transfer data to and from main memory without routing every byte through the CPU, freeing the processor for other work. Computer Architecture
DNS The phone book of the internet — translates human-readable names like example.com into IP addresses. Networks and Internet
Document Store A NoSQL database that stores data as self-contained documents (usually JSON), each holding nested fields and arrays, instead of rows split across relational tables. Data and Databases
Domain-Driven Design A software design approach centred on modelling the business domain — using a shared language between engineers and domain experts, bounded contexts to isolate models, and aggregates to enforce invariants. Software Engineering
DORA Metrics Four research-backed metrics — deployment frequency, lead time for changes, change failure rate, and mean time to restore — that predict software delivery performance and organisational outcomes. Software Engineering
Downtime Any period when a system is unavailable or not serving users correctly — the thing reliability engineering exists to minimize, measured as the inverse of uptime. Operations and Reliability
DRAM vs SRAM The two main kinds of volatile memory — DRAM is dense and cheap but slow and needs refreshing; SRAM is fast and stable but bulky and expensive, so it's used for CPU caches. Hardware

E

eBPF A Linux kernel technology that safely runs sandboxed programs inside the kernel at near-native speed — enabling programmable networking, observability, and security without writing kernel modules or rebooting. Low-Latency Systems
Edge Computing Running computation at network edge nodes — close to where users or devices are — to reduce latency, save bandwidth, and comply with data residency requirements compared to centralised cloud data centres. Applications
Electron A framework for building cross-platform desktop applications using web technologies (HTML, CSS, JavaScript) — embedding Chromium and Node.js so one codebase runs on Windows, macOS, and Linux. Applications
Elliptic Curve Cryptography Public-key cryptography using the algebraic structure of elliptic curves — providing the same security as RSA with dramatically shorter keys, making it the default for TLS, SSH, and digital signatures. Security and Privacy
Embedded System A small, special-purpose computer built into a larger product — a microwave, a car ECU, a smart thermostat, a satellite. Applications
Embedding A learned vector representation of an item — a word, an image, a user, a product — where geometric distance roughly equals semantic similarity. Artificial Intelligence
ENIAC One of the first general-purpose electronic digital computers (1945) — a room-sized machine of 18,000 vacuum tubes, programmed by physically rewiring it, that helped launch the computer age. History and Society
Erlang A functional language designed by Ericsson for fault-tolerant, distributed telephony systems — pioneering lightweight processes, message passing, and "let it crash" fault tolerance, now foundational to Elixir and modern distributed systems. Programming Languages
Error Budget The acceptable amount of downtime or errors implied by a Service Level Objective — giving teams a concrete budget to spend on reliability risk versus feature velocity, and an objective trigger for halting deployments when reliability is at risk. Operations and Reliability
Ethics in Computing The study of the moral responsibilities that come with building technology — privacy, bias, automation, safety, and the wide societal impact of the software we create. History and Society
ETL Extract, Transform, Load — the process of pulling data out of source systems, reshaping and cleaning it, and loading it into a destination like a data warehouse for analysis. Data and Databases
Eventual Consistency A consistency model where replicas of data are temporarily allowed to disagree, with the guarantee that they will converge once writes stop. Distributed Systems and Cloud

F

Feature Flag A switch in code that turns a feature on or off at runtime without a redeploy — used to roll out gradually, test in production, and decouple deploying code from releasing it to users. Software Engineering
Feature Flag Rollout A technique for enabling or disabling features at runtime without deployment — decoupling feature release from code deployment and enabling gradual rollouts, A/B tests, and instant rollbacks without redeployment. Operations and Reliability
File System The layer that organises raw storage into named files and directories, manages free space, and enforces permissions. Operating Systems
File Systems — ext4, ZFS, Btrfs Three dominant Unix file systems with different design philosophies — ext4 is stable and simple; ZFS is enterprise-grade with built-in integrity and pooled storage; Btrfs brings COW snapshots and checksums to Linux with a familiar interface. Operating Systems
Fine-Tuning Continuing to train a pre-trained model on a smaller, task-specific dataset — adapting general capabilities to a narrow domain at a fraction of the cost of training from scratch. Artificial Intelligence
Firewall A barrier that filters network traffic against a set of rules, allowing or blocking packets by address, port, or protocol to protect a network or host. Networks and Internet
Fitts's Law A predictive model of human pointing performance — time to acquire a target depends on the distance to the target and its size, expressed as T = a + b·log₂(2D/W) — guiding the design of interactive UI elements. Human-Computer Interaction
Flash Memory Non-volatile memory that stores data by trapping charge in transistor cells — retaining it without power, and the technology inside SSDs, USB sticks, and phone storage. Hardware
Floating-Point The standard way computers represent real numbers — a finite binary approximation with a sign, an exponent, and a significand that makes most arithmetic fast but never perfectly exact. Foundations
Formal Language A precisely-defined set of strings built from an alphabet according to formal rules (a grammar) — the mathematical foundation for parsing, programming languages, and computation theory. Foundations
Formal Methods Mathematical techniques for specifying, developing, and verifying software and hardware systems — using logic and proof to detect design flaws and guarantee correctness properties that testing cannot exhaustively check. Software Engineering
Formal Verification Using mathematical proof to guarantee that a system or program meets a specification — providing stronger assurance than testing by exhaustively verifying all possible behaviours. Security and Privacy
Forth A minimal, stack-based language where programs are defined as sequences of words (functions) that manipulate a data stack — notable for extreme simplicity, extensibility, and its influence on stack-based virtual machines. Programming Languages
Fourier Transform A mathematical transform that decomposes a signal into its constituent frequencies — converting between time/space domain and frequency domain — the foundation of signal processing, audio compression, image compression, and convolution. Mathematical Foundations
FPGA An integrated circuit containing an array of programmable logic blocks connected by configurable interconnects — allowing hardware circuits to be defined in software, reprogrammed after fabrication, and used for custom acceleration. Hardware
Free Software Movement The movement, launched by Richard Stallman and the Free Software Foundation, asserting users' freedom to run, study, modify, and share software — the origin of the GPL, copyleft, and the open-source ecosystem. History and Society

G

Game Engine A reusable framework for building video games — rendering, physics, audio, input, scripting, scene tools — so game teams build worlds, not engines. Applications
Game Theory The mathematical study of strategic interaction — how rational agents make decisions when the outcome for each depends on the choices of others — foundational to economics, auction design, network protocols, and AI multi-agent systems. Mathematical Foundations
Garbage Collection Automatic memory management — the runtime tracks which allocated objects are still in use and frees the rest, so programmers don't have to. Programming Languages
Gateway A network node that bridges two different networks — most commonly the "default gateway," the router that forwards traffic from your local network out to the rest of the internet. Networks and Internet
Gestalt Principles A set of perceptual principles from 1920s psychology describing how humans group visual elements — proximity, similarity, closure, continuity, and figure-ground — foundational to visual UI design. Human-Computer Interaction
Git The dominant distributed version control system. Tracks snapshots of a project's files and supports lightweight branching. Software Engineering
Go A small, garbage-collected, compiled language with first-class concurrency, designed at Google for building reliable network services. Programming Languages
Gossip Protocol A decentralised information-spreading algorithm inspired by rumour propagation — each node periodically exchanges state with a few random neighbours until information reaches the whole cluster. Distributed Systems and Cloud
GPU A processor designed for massive data-parallel work — originally for rendering graphics, now also the workhorse of machine learning, simulation, and crypto. Hardware
Grace Hopper A US Navy rear admiral and computing pioneer who built the first compiler and championed machine-independent programming languages, paving the way for COBOL and high-level programming. History and Society
Gradient Descent The optimisation algorithm that trains almost every neural network — iteratively nudge each parameter in the direction that reduces the loss. Artificial Intelligence
Graph Database A database that stores data as nodes and edges, optimising for traversal queries that follow relationships — where a relational join chain would be slow, a graph traversal is fast. Data and Databases
Graph Theory The study of graphs — collections of nodes connected by edges — which model networks, relationships, and dependencies across computing and beyond. Foundations
GUI A user interface built from visual elements you point at and manipulate — windows, icons, menus, pointers — as opposed to typing commands. Human-Computer Interaction

H

Hash Table A data structure that maps keys to values with average O(1) lookup, insert, and delete — the workhorse of dictionaries, sets, caches, and indexes. Foundations
Haskell A purely functional, lazily evaluated language with a powerful type system — notable for making side effects explicit in types, pioneering type classes, and influencing the design of Rust, Scala, Swift, and Kotlin. Programming Languages
HDD A storage device that records data magnetically on spinning platters read by a moving head — cheap per gigabyte and high-capacity, but far slower than an SSD. Hardware
HDR High Dynamic Range imaging captures and displays a wider range of luminance — from very dark to very bright — than standard displays, requiring new formats, tone mapping, and colour science to render correctly. Graphics and Media
Hexadecimal A base-16 numbering system used throughout computing because each hex digit corresponds exactly to 4 binary digits. Foundations
Hidden Markov Model A probabilistic model for sequences where an unobserved (hidden) state evolves according to a Markov chain, and each state emits an observable symbol — the foundation of speech recognition and sequence labelling. Artificial Intelligence
History of Computing A brief tour of how computing went from mechanical calculators to global cloud platforms and AI, in less than a century. History and Society
Homoiconicity A language property where code and data share the same representation — allowing programs to treat code as data structures, manipulate it programmatically, and generate new code at compile time through macros. Programming Languages
Homomorphic Encryption A form of encryption that allows arbitrary computations to be performed on ciphertext — the results, when decrypted, match what you would get if you had computed on the plaintext directly. Security and Privacy
HTTP The request/response protocol that powers the web — how browsers and servers talk to each other. Networks and Internet
HTTPS HTTP wrapped in TLS — the encrypted, authenticated version of the web's core protocol, now the default for every public site. Networks and Internet
Huge Pages Memory pages of 2 MB or 1 GB rather than the default 4 KB — reducing TLB misses for large working sets (databases, JVM heaps) by increasing the coverage each TLB entry provides, at the cost of internal fragmentation. Low-Latency Systems

I

Idempotency An operation is idempotent if performing it multiple times has the same effect as performing it once — a property that makes retries safe and distributed systems far easier to reason about. Distributed Systems and Cloud
Image Format The way pixels (and metadata) are encoded into a file — different formats trade size, quality, and feature support. Graphics and Media
Incident Response The structured way teams handle production incidents — from detection through resolution to a blameless postmortem. Operations and Reliability
Indexing Auxiliary data structures a database maintains so it can answer queries without scanning every row — the single biggest knob for query performance. Data and Databases
Information Theory The mathematics of measuring, compressing, and transmitting information — entropy quantifies surprise, and channel capacity bounds how much data any link can carry. Mathematical Foundations
Inode The on-disk record a Unix-style file system keeps for each file — everything about it except its name and its contents. Operating Systems
Instruction Set The contract between a CPU and the programs that run on it — the menu of operations a processor can perform. Computer Architecture
Integration Test A test that exercises several components together, often hitting a real database, network, or external service — slower but higher-signal than unit tests. Software Engineering
Internet History How a US defence research network became the global, public, mostly-open internet — in roughly 40 years. History and Society
Interpreter A program that reads source code (or bytecode) and executes it directly, without first producing a standalone binary. Programming Languages
Interrupt A hardware signal that pauses the CPU mid-instruction so the OS can react to an event — a keystroke, a packet, a timer tick. Operating Systems
IoT The Internet of Things — everyday physical objects embedded with sensors and network connectivity, letting them collect data and be monitored or controlled remotely. Applications
IP Address A numeric identifier for a network interface — how computers find each other on the internet. Networks and Internet
IPv6 The successor to IPv4 that expands the address space from 4 billion to 340 undecillion addresses — ending address exhaustion, simplifying routing, and building security and auto-configuration into the protocol. Networks and Internet

J

Java A statically typed, object-oriented language that compiles to bytecode and runs on the JVM — "write once, run anywhere" — long dominant in enterprise backends and Android. Programming Languages
JavaScript A dynamically typed, multi-paradigm language created for the browser, now the most-deployed runtime on Earth — browsers, Node.js, Deno, Bun, and edge platforms. Programming Languages
JPEG The most common lossy image format — it shrinks photographs dramatically by discarding visual detail the human eye barely notices, trading some quality for much smaller files. Graphics and Media
JWT A compact, self-contained token format that encodes claims as a signed JSON object — widely used for stateless authentication and authorisation between services. Security and Privacy

K

Kernel The privileged core of an operating system — the only software that talks to hardware directly and the gatekeeper that protects every program from every other. Operating Systems
Kernel Bypass A technique that allows applications to access hardware (network cards, storage) directly from userspace, bypassing the OS kernel — eliminating system call overhead, context switches, and interrupt processing to achieve single-digit microsecond latency. Low-Latency Systems
Key-Value Store A database that maps keys to values with O(1) lookup — the simplest possible data store, and the most-deployed. Data and Databases
Keyboard Shortcut A key combination that triggers a command directly, letting experienced users work faster than navigating menus — a classic trade-off between discoverability and efficiency. Human-Computer Interaction
Kubernetes An open-source container orchestrator that manages where containers run, how they're scaled, how they're networked, and how they're restarted when things break. Distributed Systems and Cloud

L

Lambda Calculus A minimal formal system for expressing computation through function abstraction and application — the mathematical foundation of functional programming, type theory, and the theoretical basis for what is computable. Foundations
Large Language Model A very large neural network — usually a transformer — trained on huge amounts of text to predict the next token. The basis of modern chat assistants and AI coding tools. Artificial Intelligence
Linear Algebra The mathematics of vectors and matrices — the language for representing and transforming data in bulk, and the engine under graphics and machine learning. Mathematical Foundations
Linear Programming Optimising a linear objective function subject to linear constraints — the foundational model for scheduling, resource allocation, and network flow, solved efficiently by the simplex method. Mathematical Foundations
Linked List A data structure built from nodes that each point to the next, allowing O(1) insert and remove at any known node — and notably awful cache behaviour. Foundations
Linus Torvalds Finnish software engineer who created the Linux kernel in 1991 and Git in 2005 — two of the most consequential software projects in history, powering smartphones, cloud servers, and distributed version control worldwide. History and Society
Lisp The second oldest high-level programming language (1958) — pioneering garbage collection, dynamic typing, the REPL, and code-as-data (homoiconicity), influencing virtually every programming language that followed. Programming Languages
Load Balancer A component that distributes incoming traffic across a pool of servers — hiding individual server failures, spreading work evenly, and making the fleet appear as a single endpoint to clients. Distributed Systems and Cloud
Lock-Free Programming Coordinating threads with atomic hardware operations instead of locks — so no thread can ever block another, eliminating lock contention and the latency spikes it causes. Low-Latency Systems
Logging Recording discrete events from a running system, so the engineers operating it can reconstruct what happened — and when, and why. Operations and Reliability
Logic Gates Tiny electronic circuits that implement boolean operations — the physical building blocks of every digital chip. Hardware

M

Machine Learning Building systems that improve at a task by learning from data instead of being explicitly programmed for every case. Artificial Intelligence
Markov Chains A stochastic process where the next state depends only on the current state — not on history — used to model random walks, PageRank, queuing systems, language models, and Monte Carlo sampling. Mathematical Foundations
Memory Fast, temporary storage where a running program keeps the data it is actively using. Hardware
Memory Hierarchy The layered set of storage in a computer — from registers to disk — trading size for speed. Computer Architecture
Memory Management How a running program acquires and releases memory — the stack and the heap, allocation and freeing, and the strategies (manual, GC, ownership) that prevent leaks and corruption. Programming Languages
Memory Pool Pre-allocating a block of memory and handing out fixed-size chunks from it — trading flexibility for speed and predictability by sidestepping the general-purpose allocator. Low-Latency Systems
Message Queue A durable middleman that lets services send and receive messages asynchronously — decoupling producers from consumers, smoothing load, and surviving outages. Distributed Systems and Cloud
Microkernel vs Monolithic Kernel The central design trade-off in operating system kernels — whether OS services run in privileged kernel space (monolithic) or as isolated user-space servers (microkernel), with different reliability, performance, and security implications. Operating Systems
Microservices An architectural style that builds an application as many small, independently-deployable services, each owning its own data and talking over a network. Distributed Systems and Cloud
Mob Programming A practice where the entire team works together at a single workstation on one task at a time — an extreme form of pair programming scaled to the whole team, maximising knowledge sharing and collective code ownership. Software Engineering
Mobile App Software designed to run on a phone or tablet — distributed through an app store and sandboxed by the platform. Applications
Monitoring Continuously observing a running system — collecting metrics, alerting on anomalies — so problems are caught before users notice. Operations and Reliability
Monorepo A single version-control repository that holds many projects or services together — sharing tooling, dependencies, and atomic cross-project changes — instead of splitting each into its own repo. Software Engineering
Moore's Law Gordon Moore's 1965 observation that the number of transistors on a chip doubles roughly every two years — the empirical trend that drove 50 years of computer performance improvements and is now slowing. Hardware
Motherboard The main circuit board that connects and powers every component of a computer — CPU, memory, storage, and peripherals — and lets them communicate over shared buses. Hardware
MPI Basics The standard API for parallel programs that run across many compute nodes, communicating by explicitly sending and receiving messages — the infrastructure behind most scientific supercomputing. Distributed Systems and Cloud
MPLS A routing technique that forwards packets by swapping short labels instead of looking up IP addresses — enabling traffic engineering, VPNs, and predictable paths across carrier networks. Networks and Internet
Multi-Factor Authentication Requiring two or more independent proofs of identity before granting access — so a stolen password alone cannot compromise an account. Security and Privacy
Multimodal AI AI systems that process and generate across multiple modalities — text, images, audio, and video — in a single model, enabling tasks like image captioning, visual question answering, and audio transcription. Artificial Intelligence
Mutex A synchronization primitive that ensures only one thread at a time can hold it — the basic tool for protecting shared state from data races. Operating Systems
MVCC A concurrency technique where writes create new versions of rows rather than overwriting them — readers see a consistent snapshot of the past while writers proceed concurrently, with no read/write blocking. Data and Databases

N

NAT Network Address Translation — how a router lets many devices on a private network share one public IP address by rewriting addresses and ports on traffic passing through it. Networks and Internet
Native vs Web The core decision in app development — build a native app installed per platform, a web app that runs in the browser, or a hybrid that blends the two — each trading reach against capability and performance. Applications
Natural Language Processing The field of getting computers to understand, generate, and work with human language — from spam filters and translation to the large language models behind modern chatbots. Artificial Intelligence
Neural Network A family of machine learning models loosely inspired by the brain — layers of simple units that, together, can approximate complex functions. Artificial Intelligence
Normalization A discipline for arranging tables to eliminate redundancy and update anomalies — the design counterpart to the relational model. Data and Databases
NoSQL An umbrella term for databases that don't follow the relational model — key-value stores, document stores, wide-column stores, graph databases. Data and Databases
NUMA Awareness On multi-socket servers each CPU has fast local memory and slow remote memory — NUMA-aware code allocates memory on the same socket as the thread that uses it, halving memory latency. Low-Latency Systems
Numerical Methods Algorithms for computing approximate answers to mathematical problems a computer cannot solve exactly — root-finding, integration, solving differential equations, and fitting data. Mathematical Foundations

O

OAuth A standard for delegated authorization — letting an app act on a user's behalf at another service without ever seeing the user's password. Security and Privacy
Observability The ability to understand a system's internal state from the data it emits — metrics, logs, and traces — so you can debug problems you didn't anticipate, not just the ones you alerted on. Operations and Reliability
OpenMP A set of compiler directives and library routines for shared-memory parallelism in C, C++, and Fortran — add a pragma above a loop and the compiler parallelises it across all cores on one machine. Distributed Systems and Cloud
Operating System The system software that manages hardware and provides services and abstractions to all other programs. Operating Systems
Optimization Theory The mathematical study of choosing the best solution from a set of feasible alternatives — minimising or maximising an objective function subject to constraints — underpinning machine learning, operations research, and engineering design. Mathematical Foundations
ORM A library that maps rows in a relational database to objects in your programming language, so you can query with code instead of SQL strings. Data and Databases
OSI Model A seven-layer conceptual model for how networking protocols stack on top of each other — physical wires at the bottom, applications at the top. Networks and Internet
Out-of-Order Execution A CPU technique that executes instructions as soon as their inputs are ready rather than in strict program order, keeping execution units busy while slow operations like memory loads complete. Computer Architecture

P

Package Manager A tool that automates downloading, installing, updating, and resolving dependencies of software packages — making it practical to build on a foundation of third-party libraries without manually managing files and versions. Software Engineering
Packet A small, self-describing chunk of data that travels across a network. The internet's fundamental unit of communication. Networks and Internet
Paging The mechanism that moves fixed-size pages of memory between RAM and disk on demand — the engine inside virtual memory. Operating Systems
Parsing Turning a stream of characters into a structured tree a program can analyse — the front-end of every compiler, query engine, and data format. Programming Languages
Password Hashing One-way, deliberately slow transformations of a password used so that a database breach doesn't reveal the originals. Security and Privacy
Paxos The foundational consensus algorithm that proved distributed agreement is possible in the face of message loss and crashes — notoriously hard to understand, but the theoretical backbone of nearly all consensus work. Distributed Systems and Cloud
Perceptron The original artificial neuron — a single unit that takes weighted inputs, applies a threshold, and outputs a binary decision. The simplest learnable classifier and the ancestor of modern neural networks. Artificial Intelligence
Peripheral Any device attached to a computer that isn't the core CPU and memory — keyboards, mice, displays, printers, drives, cameras — through which the machine takes input and produces output. Hardware
Pixel The smallest addressable element of a digital image — a tiny coloured square that, together with billions of others, makes up what you see on a screen. Graphics and Media
PNG A lossless image format that preserves every pixel exactly and supports transparency — ideal for graphics, logos, screenshots, and text, where JPEG's lossy compression would smear detail. Graphics and Media
Pointer and Reference A value that stores the memory address of another value — the fundamental mechanism for indirection, dynamic memory, linked data structures, and passing large objects efficiently. Programming Languages
Post-Quantum Cryptography Cryptographic algorithms designed to resist attacks from quantum computers — replacing RSA and ECC which are broken by Shor's algorithm, using hard problems like Learning With Errors that have no known quantum speedup. Security and Privacy
Probability and Statistics The mathematics of uncertainty and evidence — probability models what might happen, statistics infers what is true from data. Together they underpin machine learning and analytics. Mathematical Foundations
Process A running instance of a program, with its own memory, file handles, and CPU time — the unit the operating system schedules and isolates. Operating Systems
Programming Language A formal language for instructing computers — the human side of software. Programming Languages
Progressive Web App A web application enhanced with service workers and a web manifest to provide app-like capabilities — installability, offline access, push notifications, and near-native performance — without requiring an app store. Applications
Prompt Engineering The craft of designing inputs to a language model to reliably elicit the desired output — through clear instructions, examples, role-setting, and structured reasoning techniques. Artificial Intelligence
Public-Key Cryptography Cryptography using a pair of mathematically linked keys — one you share, one you keep secret. The basis of TLS, signatures, and modern authentication. Security and Privacy
Python A general-purpose, dynamically typed, interpreted programming language known for readable syntax and a vast ecosystem. Programming Languages

Q

Query Plan The step-by-step program a database derives from your SQL query before executing it — the lever you use to diagnose and fix slow queries. Data and Databases
QUIC A transport protocol built on UDP that combines TCP's reliability with TLS's encryption in a single handshake — eliminating head-of-line blocking and reducing connection setup latency. Networks and Internet

R

Raft A consensus algorithm designed to be understandable — it achieves distributed agreement through leader election and log replication, and has become the go-to replacement for Paxos in modern systems. Distributed Systems and Cloud
Rasterization The technique of turning vector shapes (triangles, lines, text) into pixels — the dominant way real-time 3D graphics get drawn. Graphics and Media
Rate Limiting Controlling how many requests a client or service can make in a time window — protecting backends from overload, preventing abuse, and enforcing fair use across tenants. Distributed Systems and Cloud
Ray Tracing A rendering technique that simulates light by tracing the paths of rays through a scene — producing physically accurate reflections, shadows, and lighting at a high computational cost. Graphics and Media
RDMA A technology that allows one computer to directly read or write another computer's memory over a network — bypassing both CPUs — achieving ~1 µs latency and near-line-rate bandwidth for distributed computing, ML training, and storage. Low-Latency Systems
Real-Time Operating System An operating system that guarantees tasks complete within specified time bounds — critical for embedded systems, robotics, and safety-critical applications where missing a deadline is as bad as an incorrect result. Operating Systems
Real-Time Systems Systems where the correctness of a computation depends not only on its result but on the time at which it is produced — from spacecraft flight control to live video streaming, each with different deadline strictness requirements. Applications
Recursion A way of solving a problem by having a function call itself on a smaller version of the same problem, until the base case is trivial. Foundations
Refactoring Improving the internal structure of code without changing its external behaviour — the way you keep a codebase from rotting. Software Engineering
Register A handful of tiny, lightning-fast storage cells inside the CPU — the only memory most instructions actually read from or write to. Computer Architecture
Regular Expression A formal notation for describing patterns in text — based on the theory of finite automata and regular languages, implemented in every programming language for string matching, validation, and parsing. Foundations
Reinforcement Learning A branch of machine learning where an agent learns to act in an environment by trial-and-error, optimising a reward signal. Artificial Intelligence
Relational Model A model of data as a set of relations (tables of tuples) — the mathematical foundation under SQL databases. Data and Databases
Replication Keeping copies of the same data on multiple machines for availability, durability, and read scaling. Distributed Systems and Cloud
REST API An architectural style for HTTP-based APIs that models the world as named resources accessed via standard verbs — the dominant way services talk to each other on the web. Networks and Internet
Retrieval-Augmented Generation A technique that improves language model answers by first fetching relevant documents from a knowledge base, then generating a response conditioned on both the query and the retrieved content. Artificial Intelligence
RISC vs CISC Two philosophies of CPU instruction set design — Reduced Instruction Set Computing (small, simple, fast) versus Complex Instruction Set Computing (rich, do-more-per-instruction). Computer Architecture
Router A device that forwards IP packets between networks, deciding which neighbour gets each packet on its way to the destination. Networks and Internet
Runbook A documented, step-by-step procedure for handling a specific operational task or failure — so any on-call engineer can respond correctly under pressure without reinventing the fix. Operations and Reliability
Rust A modern systems language with C-like performance, no garbage collector, and a borrow checker that guarantees memory safety at compile time. Programming Languages

S

Saga Pattern A pattern for managing long-lived distributed transactions by breaking them into a sequence of local transactions, each with a compensating action to undo it if a later step fails. Distributed Systems and Cloud
Sandbox A security mechanism that restricts a process to a minimal set of resources and capabilities — so that exploiting a vulnerability in a sandboxed process still cannot compromise the wider system. Security and Privacy
Scheduler The part of the OS kernel that decides which thread runs on each CPU at any moment — balancing fairness, responsiveness, and throughput. Operating Systems
Schema Migration The disciplined, versioned process of changing a database's structure — adding columns, tables, or indexes — over time, in step with the application, without losing data or downtime. Data and Databases
Scientific Computing Using computers to model, simulate, and analyze scientific and engineering problems — from weather forecasts to drug discovery — through numerical methods running on everything from laptops to supercomputers. Applications
Semantic Versioning A convention for version numbers — MAJOR.MINOR.PATCH — where each part signals the kind of change (breaking, feature, fix), so the people who depend on your software can update safely. Software Engineering
Semaphore A signalling mechanism that controls access to shared resources by maintaining a counter — threads decrement it to acquire a resource and increment it to release, blocking when the count reaches zero. Operating Systems
Serverless A deployment model where you write functions or small services and the platform handles provisioning, scaling, and idling them — you pay per-request, not per-server. Distributed Systems and Cloud
Service Mesh An infrastructure layer that handles service-to-service communication for microservices — routing, retries, encryption, and observability — usually via sidecar proxies, so application code doesn't have to. Distributed Systems and Cloud
Set Theory The mathematics of collections — sets, membership, and the operations on them. The shared vocabulary beneath logic, databases, type systems, and the rest of mathematics. Mathematical Foundations
Shader A small program that runs on the GPU to compute how geometry and pixels are drawn — controlling position, color, lighting, and effects — executed in parallel across millions of elements. Graphics and Media
Sharding Splitting data across multiple machines by some key, so the working set per machine — and the request load — stays manageable as the system grows. Distributed Systems and Cloud
Shell The program that reads the commands you type, expands and parses them, and asks the OS to run them — the text interface between a user and the operating system. Operating Systems
Side-Channel Attack An attack that extracts secrets not by breaking an algorithm mathematically but by observing physical or measurable side effects of its execution — timing, cache access patterns, power consumption, or electromagnetic emissions. Security and Privacy
SIMD Single Instruction, Multiple Data — a CPU feature that applies one operation to many data elements at once, accelerating the vector and array math common in graphics, media, and machine learning. Computer Architecture
SIMD Intrinsics C/C++ functions that map directly to vector CPU instructions — bypassing the auto-vectoriser to write hand-tuned code that processes 4, 8, or 16 values in a single clock cycle. Low-Latency Systems
SLO, SLI, SLA The vocabulary of reliability targets — an SLI measures how well a service is doing, an SLO is the goal for that measure, and an SLA is the contractual promise (with penalties) to a customer. Operations and Reliability
Smalltalk The language that invented modern object-oriented programming — Alan Kay's vision of objects communicating purely via message passing, pioneering the GUI, the REPL, live programming environments, and the MVC pattern. Programming Languages
Socket The OS abstraction that lets a program send and receive data over a network — the fundamental API sitting between application code and the TCP/IP stack. Networks and Internet
Speculative Execution A CPU technique that executes instructions before knowing whether they will be needed — predicting branches and precomputing results to keep execution units busy, with disastrous security consequences when exploited by Spectre-class attacks. Computer Architecture
Spreadsheet A grid of cells holding data and formulas that recalculate automatically — the world's most widely used programming tool, even though most users don't think of it as programming. Applications
SQL A declarative language for querying and manipulating relational databases — you say what you want, the database figures out how. Data and Databases
SQL Injection A vulnerability where attacker-controlled input is concatenated into a SQL query, letting them rewrite it to read, modify, or destroy any data the app can access. Security and Privacy
SRE A discipline pioneered at Google that applies software-engineering principles to operations — automation, SLOs, error budgets, blameless culture. Operations and Reliability
SSD A storage device that keeps data in flash memory chips with no moving parts — far faster than a spinning hard drive, and now the default storage in most computers. Hardware
Stack and Queue Two of the simplest data structures — a stack is last-in-first-out, a queue is first-in-first-out. Both show up everywhere from CPU instructions to background job systems. Foundations
Storage Long-term, non-volatile storage where files and programs are kept when the computer is off. Hardware
Subpixel Rendering A text rendering technique that exploits the individual RGB subpixels of an LCD display to increase apparent horizontal resolution — making text appear crisper and more readable at small font sizes. Graphics and Media
Superscalar Execution A CPU design that issues multiple independent instructions per clock cycle by maintaining several execution units in parallel — extracting instruction-level parallelism (ILP) from sequential code automatically. Computer Architecture
Supervised Learning Learning a function from labelled examples — the most widely-deployed flavour of machine learning. Artificial Intelligence
Support Vector Machine A classifier that finds the widest possible margin between classes — supported by the training points closest to the boundary, with kernels extending it to non-linear problems. Artificial Intelligence
Syntax vs Semantics Syntax is the grammar — which arrangements of symbols are legal; semantics is the meaning — what a legal program actually does when it runs. Programming Languages
System Call The mechanism a user-space program uses to ask the OS kernel to do something privileged — open a file, send a packet, allocate memory, fork a process. Operating Systems
Systolic Array A grid of simple processing elements that pass data between neighbours in a rhythmic, pipelined fashion — used in neural network accelerators (Google TPU) to perform dense matrix multiplications with extreme efficiency. Computer Architecture

T

TCP A reliable, ordered, stream-based transport protocol on top of IP. The plumbing under most internet traffic. Networks and Internet
Technical Debt A metaphor for the long-term cost of cutting corners — small short-term wins that compound into a heavy maintenance burden. Software Engineering
Test-Driven Development A development practice where you write a failing test before writing any production code — driving design through tests and ensuring every feature is covered, with the red-green-refactor cycle as the rhythm of work. Software Engineering
Testing Writing code that runs your code to check it does what it should — the safety net that lets teams change software without breaking it. Software Engineering
Thread A single line of execution inside a process — the unit the CPU actually runs. A process can have many threads that share memory. Operating Systems
Threat Model A structured way to think about who might attack a system, what they want, what they can do, and what defences make sense — done before bugs, not after. Security and Privacy
Tim Berners-Lee British scientist who invented the World Wide Web in 1989 at CERN — proposing HTTP, HTML, and URLs as an open, non-proprietary system for sharing information, then deliberately not patenting it to ensure universal access. History and Society
Time-Series Database A database optimised for storing and querying sequences of timestamped values — metrics, sensor readings, financial ticks — with compression and downsampling built in for the patterns time-series data exhibits. Data and Databases
TLB A small, fast cache for virtual-to-physical address translations — avoiding the costly page table walk on every memory access and making virtual memory practical at CPU speed. Computer Architecture
TLS The protocol that encrypts and authenticates almost all secure traffic on the internet — the "S" in HTTPS, IMAPS, SMTPS, and many more. Networks and Internet
Toil Manual, repetitive, automatable operational work that grows with service scale — Google's SRE model defines toil as the enemy of engineering productivity and mandates that SREs spend no more than 50% of their time on it. Operations and Reliability
Touch Interface An interface operated by touching the screen directly with fingers — using taps, swipes, and gestures instead of a mouse and keyboard — the dominant way people interact with phones and tablets. Human-Computer Interaction
TPU Google's custom ASIC for accelerating machine learning workloads — a matrix multiplication engine built as a systolic array, providing far higher throughput and power efficiency than GPUs for transformer and convolution operations. Hardware
Training and Inference The two distinct phases of a machine-learning model's life — learning its parameters (training) and using them to make predictions (inference). Artificial Intelligence
Transformer The neural-network architecture, introduced in 2017, that powers modern large language models, image generation, and most of contemporary AI. Artificial Intelligence
Transistor The microscopic electronic switch that, replicated by the billions, forms every modern integrated circuit and CPU. Hardware
Tree A hierarchical data structure where each node has children but only one parent — the basis of file systems, search structures, DOMs, and ASTs. Foundations
Turing Machine An imaginary computer with an infinite tape and a tiny rule book — the model that defines what is computable. History and Society
Type System A set of rules a programming language uses to assign and check the "kinds" of values, catching whole classes of bugs before the program runs. Programming Languages
Type Theory A formal framework for classifying values by their kind — preventing invalid operations, enabling type inference, and at its most powerful, encoding mathematical proofs as programs through the Curry-Howard correspondence. Foundations

U

UDP A connectionless, "fire and forget" transport protocol. Faster than TCP but with no delivery, ordering, or reliability guarantees. Networks and Internet
Unit Test A small, fast test that exercises one unit (function, class, module) in isolation — the foundation of the testing pyramid. Software Engineering
Unix History The story of Unix — from a 1969 Bell Labs side project to the common ancestor of Linux, macOS, the BSDs, Android, and iOS — and the design philosophy that shaped modern computing. History and Society
Usability Testing Watching real people attempt real tasks with a product to discover where they struggle — the most direct way to find out whether a design actually works. Human-Computer Interaction
User Interface The surface where a person and a computer meet — what users see, touch, hear, and act on. Human-Computer Interaction
UX The discipline of shaping how a person feels and what they can do when using a product, system, or service. Human-Computer Interaction

V

Vector Database A database optimised for storing and searching high-dimensional embedding vectors by similarity — the storage layer behind semantic search and retrieval-augmented generation. Data and Databases
Version Control Tracking changes to code (and other files) over time, so teams can collaborate without trampling each other's work. Software Engineering
Video Codec An encoder/decoder that compresses video by exploiting redundancy within and between frames — the reason streaming and storing high-resolution video is feasible at all. Graphics and Media
Virtual Memory A technique that gives each process the illusion of a private, contiguous memory space — built from page tables that map virtual addresses to physical RAM. Operating Systems
Virtualization Running multiple isolated operating systems simultaneously on a single physical machine by intercepting privileged operations and presenting each OS with a virtual hardware interface. Operating Systems
Vulnerability A flaw in software or its configuration that an attacker can exploit to violate a system's security — plus the lifecycle of finding, disclosing, tracking, and patching it. Security and Privacy

W

Wasm Runtime A server-side WebAssembly execution environment that runs Wasm binaries outside the browser — enabling sandboxed, portable, polyglot compute for serverless functions, plugins, and edge workloads. Applications
Web Browser A program that fetches web pages over HTTP, parses HTML/CSS/JavaScript, and renders them as the interactive sites you see. Applications
WebAssembly A portable binary instruction format that runs at near-native speed in browsers and on servers — enabling C, C++, Rust, and other languages to run on the web without JavaScript, and serving as a universal sandboxed compute target beyond the browser. Applications
WebSocket A protocol that upgrades an HTTP connection into a full-duplex, persistent channel for sending messages back and forth in real time. Networks and Internet
Write-Ahead Log A durability mechanism where every change is written to an append-only log before it is applied to the main data files — if the system crashes, the log is replayed to recover to the last committed state. Data and Databases

X

Xerox PARC Xerox's legendary research laboratory (1970–) that invented the graphical user interface, Ethernet, laser printing, object-oriented programming (Smalltalk), and WYSIWYG editing — shaping every personal computer, operating system, and office printer since. History and Society
XSS Cross-Site Scripting — a vulnerability where an attacker injects malicious JavaScript into a page that other users then run as if it came from the site. Security and Privacy

Z

Zero Trust A security model that trusts no network location by default — every request must be authenticated, authorized, and encrypted, whether it comes from outside the network or inside it. Security and Privacy