Glossary

A friendly dictionary of web terms — the jargon, decoded.

API: Application Programming Interface — a contract that lets one piece of software talk to another. On the web, usually means an HTTP endpoint that returns JSON.
ARIA: Accessible Rich Internet Applications — a set of HTML attributes that describe interactive widgets to assistive technologies.
Async: Code that doesn't block while waiting for a result. In JavaScript, expressed with Promises, async functions, and the await keyword.
Bundler: A build tool that combines many source files into a smaller number of optimized files for the browser. Examples: Vite, esbuild, Webpack.
Cache: Stored copy of a previously computed or fetched value, kept to avoid the cost of recomputing or refetching.
Callback: A function passed to another function to be called later, typically when an event happens or async work finishes.
Cascade: The CSS algorithm that decides which rule wins when multiple rules target the same element. Considers origin, specificity, and source order.
CDN: Content Delivery Network — a global network of servers that caches your static assets close to users for faster delivery.
Closure: A function that remembers the variables from the scope it was created in, even after that scope has finished executing.
CLS: Cumulative Layout Shift — a Core Web Vital that measures how much page content unexpectedly moves around as it loads.
CORS: Cross-Origin Resource Sharing — browser security policy that controls which origins can fetch data from your API.
CSS Grid: A two-dimensional CSS layout system for arranging elements in rows and columns simultaneously.
DOM: Document Object Model — the in-memory tree of elements the browser builds from your HTML.
DRY: Don't Repeat Yourself — programming principle that says every piece of knowledge should have a single representation in code.
Endpoint: A specific URL on an API that performs one operation, like GET /users/123 or POST /orders.
ES module: The official JavaScript module format using import and export statements. Replaces older CommonJS require().
Flexbox: A one-dimensional CSS layout system for distributing space along a single axis (row or column).
Hoisting: JavaScript behavior where variable and function declarations are conceptually moved to the top of their scope before execution.
HTTP: HyperText Transfer Protocol — the request/response protocol the web is built on.
Hydration: The process by which client-side JavaScript attaches behavior to server-rendered HTML, making it interactive.
iframe: An HTML element that embeds another HTML document inside the current one. Used here to render your live preview.
JSON: JavaScript Object Notation — a lightweight text format for exchanging structured data. The web's lingua franca.
Lazy loading: Deferring the loading of a resource until it's actually needed, usually to speed up initial page load.
LCP: Largest Contentful Paint — a Core Web Vital that measures when the largest above-the-fold element finishes rendering.
Media query: A CSS feature that applies styles conditionally based on viewport width, device type, color scheme, or motion preference.
Promise: A JavaScript object representing the eventual result of an asynchronous operation.
REST: An architectural style for HTTP APIs that maps CRUD operations to standard HTTP verbs (GET, POST, PUT, DELETE).
Selector: The part of a CSS rule that decides which HTML elements the rule applies to.
Specificity: How CSS calculates which rule wins when multiple rules target the same element. More specific selectors override less specific ones.
SSR: Server-Side Rendering — generating HTML on the server before sending it to the browser, for faster first paint and better SEO.
Viewport: The visible area of a web page inside the browser window. Its width and height drive responsive design.