Plain-language definitions of the terms this site — and the accessibility field — use constantly. Each one says what it means and why it matters. No jargon. New to accessibility? Start with our plain-language introduction.
- Accessibility (web accessibility)
- Websites and apps that everyone can use, including people with disabilities.
- Why it matters: Accessibility removes barriers so no one is locked out.
- WCAG
- Web Content Accessibility Guidelines — the international standard for web accessibility.
- Why it matters: It is the rulebook most accessibility laws and policies point to.
- See the WCAG criteria →
- Success criterion (SC)
- A single, testable rule in WCAG, such as “images must have a text alternative”.
- Why it matters: Each one is a specific thing you can check on a page.
- Browse all criteria →
- POUR
- The four principles WCAG is built on: Perceivable, Operable, Understandable, Robust.
- Why it matters: It is a simple way to group every rule in the standard.
- Level A / AA / AAA
- The three levels of WCAG conformance, from basic (A) to highest (AAA).
- Why it matters: Most laws and policies ask for level AA. This site itself targets AAA.
- Alt text (text alternative)
- A short written description of an image, read aloud by screen readers.
- Why it matters: It tells people who cannot see the image what it shows.
- Screen reader
- Software that reads the screen aloud for people who are blind or have low vision.
- Why it matters: It is one of the main tools people use to browse the web.
- Assistive technology
- Any tool that helps a person with a disability use the web — a screen reader, magnifier, switch device, or voice control.
- Why it matters: Good websites work with these tools, not against them.
- Keyboard accessible
- Everything on the page can be used with a keyboard alone — no mouse needed.
- Why it matters: Many people navigate by keyboard, switch device, or voice control.
- Focus indicator
- The visible outline that shows where you are on the page when using a keyboard.
- Why it matters: Without it, keyboard users get lost.
- Color contrast ratio
- A measure of how different the text color is from its background.
- Why it matters: Low contrast makes text hard to read, especially for people with low vision.
- Landmark
- A labeled region of a page, such as the header, navigation, or main content.
- Why it matters: Screen-reader users jump between landmarks to find things fast.
- Heading structure
- Using real headings (h1, h2, h3) in the right order to outline the page.
- Why it matters: It is how screen-reader users skim and navigate.
- ARIA
- A set of HTML attributes that add accessibility information to custom controls.
- Why it matters: Used carefully it fills gaps HTML alone cannot — but native HTML always comes first.
- Conformance
- How well a site meets WCAG — whether it passes, fails, or needs human review.
- Why it matters: It is the honest measure of where your site stands.
- Automated test
- A check run by software, with no human judgement.
- Why it matters: Fast and consistent, but it can only catch part of the picture.
- Manual test
- A check done by a person, such as testing with a keyboard or a screen reader.
- Why it matters: Some things only a human can judge.
- AI-assisted review
- Using AI to help check the things automation alone cannot decide.
- Why it matters: It narrows the gap, but a person still confirms the result — it is not proof.
- VPAT / ACR
- A VPAT is a blank accessibility report template; a completed one is an Accessibility Conformance Report (ACR).
- Why it matters: Buyers, funders, and procurement teams often ask for one.
- About independent review →
- WCAG-EM
- The official step-by-step method for evaluating a website against WCAG.
- Why it matters: It is how a credible, repeatable audit is done.
- Our methodology →
- Section 508
- A United States law requiring federal websites to be accessible.
- Why it matters: It maps to WCAG 2.0 AA.
- See regulations →
- EN 301 549
- The European accessibility standard for digital products and services.
- Why it matters: It is the EU's equivalent, also based on WCAG.
- See regulations →
