Web terms, explained
Plain explanations of the words that turn up in quotes, audits and Search Console — written from projects rather than from a spec sheet.
20 terms
Accessibility
What the standards require, what a tool can check for you, and what only a person can.
contrast ratio
The measured difference between text and its background
Contrast ratio is the measured difference in relative luminance between text and its background, from 1:1 to 21:1. WCAG asks for at least 4.5:1 for normal text, 3:1 for large text, and 3:1 for the parts of a control that convey what it is.
WCAG
Web Content Accessibility Guidelines
WCAG is the W3C standard for making web content usable by people with disabilities. It defines three conformance levels — A, AA and AAA — and AA is the one European law, public tenders and corporate contracts actually ask for.
Performance
The numbers Google measures on real visits, and what actually moves them.
CDN
Content Delivery Network
A CDN is a network of servers around the world that keep copies of your site and answer visitors from whichever one is nearest. It removes the distance between the visitor and the origin server — and only that.
CLS
Cumulative Layout Shift
CLS scores how much a page jumps around while it loads, on a unitless scale where 0.1 or less is good. Every element that moves without the visitor causing it adds to the score, weighted by how far it moved and how much of the screen it took.
Core Web Vitals
Google's page experience metrics
Core Web Vitals are the three metrics Google collects from real Chrome visits: LCP for loading, INP for responsiveness and CLS for visual stability. A URL passes when 75% of its visits are inside the good threshold.
INP
Interaction to Next Paint
INP measures how long a page takes to paint a response after a tap, click or key press. Good is 200 milliseconds or less. It replaced FID in March 2024 and, unlike FID, it watches every interaction rather than only the first.
LCP
Largest Contentful Paint
LCP measures when the largest element in the viewport finishes rendering — usually the hero image or the headline. Google calls 2.5 seconds or less good, measured on real visits at the 75th percentile.
SEO and AI search
How a page is found, cited and quoted — by a search engine and by a model.
AEO
Answer Engine Optimization
AEO is the work of making a page usable as a source by systems that answer questions directly — AI assistants and AI overviews — rather than only listing links. The goal shifts from being clicked to being quoted correctly and attributed.
canonical URL
The address a page declares as its own
A canonical URL is the address a page names as the real one for its content, so a search engine that reaches it by any other route indexes the named version instead. It is a strong hint, not an instruction, and Google can overrule it.
Google Search Console
Google's reporting tool for site owners
Search Console is the free tool where Google reports what it knows about your site: which queries showed it, where it ranked, which pages are indexed and which are not, and what its crawler found wrong. It is the only first-party source for any of it.
hreflang
Language annotation for pages that exist in more than one language
An hreflang annotation tells a search engine that two pages are the same document in different languages. It only works when both sides name each other and each one names itself — a one-sided set is discarded for the whole cluster.
llms.txt
A proposed index file for language models
An `llms.txt` is a Markdown file at the root of a site that lists its important pages with a sentence about each, meant to be read by language models rather than by browsers. It is a community proposal, not a standard any crawler has committed to.
structured data
Machine-readable description of what a page is about
Structured data is a block of machine-readable facts added to a page — what it is, who wrote it, what it costs — using the schema.org vocabulary, usually as JSON-LD. Search engines read it to understand the page and sometimes to decorate the result.
Technology
The words on a quote: what they mean, what they cost and when they are the wrong choice.
Astro
The web framework this site is built with
Astro is a web framework that renders pages to HTML at build time and ships no JavaScript unless a component asks for it. Interactive pieces are declared one by one as islands, so a page carries the code for those and nothing else.
CMS
Content Management System
A CMS is the software that lets someone change a website without touching code. The word covers three separate jobs — editing, storing and displaying content — and most arguments about which CMS to use are really arguments about which of the three you need.
headless CMS
Content management system without a front end
A headless CMS stores and edits content but does not render the website. The pages are built by something else, which reads the content over an API — so the editing tools and the front end can be changed independently of each other.
Laravel
PHP framework for web applications
Laravel is a PHP framework for building web applications — the kind with accounts, permissions, a database and work that runs in the background. It supplies the parts every application needs so they are not rebuilt by hand on each project.
SSG
Static site generation
Static site generation builds every page into a finished HTML file before anyone visits, so a request is answered by a file server instead of by code, a database query and a template rendered on the spot.
Vue
Vue.js
Vue is a JavaScript framework for building interfaces out of components whose display updates automatically when their data changes. It can run a whole application or a single widget inside a page that is otherwise plain HTML.
Law and obligations
What binds a website owner, from when, and who it actually applies to.
European Accessibility Act
Directive (EU) 2019/882
The European Accessibility Act is an EU directive that requires certain products and services — e-commerce among them — to be accessible to people with disabilities. National implementations have applied since 28 June 2025, and for websites the technical reference is WCAG 2.1 level AA.