Accessibility glossary

Plain-language definitions of the words you will meet in accessibility work, with links to the standards and laws they come from.

People and technology

Accessibility: People can find, understand, and use your website, app, or documents, whatever their abilities and whatever they use to browse.
Accessibility tree: The structure a browser builds from a page that screen readers and AI agents read to understand it.
AI agent: An AI assistant that browses websites and completes tasks on a person’s behalf, reading pages through the accessibility tree.
Assistive technology: Hardware or software a person uses to do what a standard setup makes hard, such as a screen reader or a switch.
Audio description: A narration track that describes what is happening on screen for people who cannot see the video.
Braille display: A device with a row of pins that rise and fall to show text as braille, driven by a screen reader.
Captions: Text shown on a video that gives the dialogue and important sounds in time with the picture.
Cognitive accessibility: Design that works for people with differences in attention, memory, reading, or processing, which helps everyone.
Color vision deficiency: Difficulty telling certain colors apart, most often red and green, which is common and mostly inherited.
Keyboard navigation: Moving through and operating a page with the keyboard alone, mostly with Tab, Enter, Space, and the arrow keys.
Low vision: Vision that cannot be fully corrected with glasses, so a person needs larger text, more contrast, or magnification.
Screen magnifier: Software that enlarges part of the screen so a person with low vision can read it.
Screen reader: Software that reads what is on the screen aloud or sends it to a braille display.
Switch access: A way of operating a device with one or more buttons, for people who cannot use a keyboard or touchscreen.
Temporary and situational disability: A short-term or circumstantial limit, such as a broken arm or bright sunlight, that creates the same barriers a permanent disability does.
Transcript: A text version of an audio or video recording that a person can read instead of listening.
Voice control: Operating a device by speaking commands, such as the name of a button to press.

Standards and techniques

Accessible name: The name a control is announced by, taken from its label, its text, or its alt text.
Alt text: The written description of an image that a screen reader reads aloud and a search engine indexes.
ARIA: A set of HTML attributes that tell assistive technology what a custom control is, what it is called, and what state it is in.
Color contrast: The difference in brightness between text and its background, measured as a ratio that WCAG sets minimums for.
Conformance level: WCAG’s three tiers of requirements, A, AA, and AAA, where Level AA is what laws and contracts ask for.
EN 301 549: The European standard for accessible technology, whose web requirements follow WCAG 2.1 Level AA.
Error identification: Telling a person which form field has a problem and what to do about it, in text, next to the field.
Focus indicator: The visible outline or highlight that shows which element the keyboard is on.
Form label: The visible text tied to a form field in the code, so assistive technology announces what the field is for.
Heading structure: Headings that outline the page in order, one main heading and then levels that nest without skipping.
Keyboard trap: A part of a page that keyboard focus can enter but not leave, so someone using a keyboard is stuck.
Landmark: A labeled region of a page, such as the main content or the navigation, that assistive technology can jump to.
Live region: A part of a page marked so that screen readers announce its changes without the person leaving where they are.
Plain language: Writing that the intended reader can understand the first time, with common words, short sentences, and a clear structure.
POUR: The four WCAG principles, perceivable, operable, understandable, and robust, remembered by their first letters.
Reduced motion: A system setting that asks websites and apps to cut animation, which some people need to avoid dizziness or distraction.
Reflow: A layout that rearranges into one column when the window is narrow or the page is zoomed, with no sideways scrolling.
Semantic HTML: Using the HTML element that means what the content is, such as a button for a button, so browsers and assistive technology understand it.
Skip link: A link at the top of a page that lets people using a keyboard jump past the navigation to the main content.
Success criterion: One testable requirement in WCAG, with a number, a level, and a plain statement of what must be true.
Tagged PDF: A PDF with a hidden structure of headings, lists, tables, and alt text that lets a screen reader read it in order.
Target size: How big a button, link, or other control is on screen, which decides whether people can tap it reliably.
Text spacing: The ability of a page to stay readable when a person increases line height, letter spacing, and paragraph spacing.
Timeout: A limit on how long a person has to finish a task before the page resets or signs them out.
WCAG: The Web Content Accessibility Guidelines, the international standard for accessible web content that most laws point at.
WCAG 2.2: The current version of the Web Content Accessibility Guidelines, a W3C Recommendation.

Laws and regulations

Accessible Canada Act: Canada’s federal accessibility law, covering federally regulated organizations such as banks, airlines, and telecoms.
ADA: The Americans with Disabilities Act, the U.S. civil rights law that the Department of Justice says applies to websites.
ADA Title II: The part of the ADA that covers state and local governments, now with a web rule naming WCAG 2.1 AA and dated deadlines.
ADA Title III: The part of the ADA that covers businesses open to the public, which the Department of Justice says includes their websites.
AODA: Ontario’s accessibility law, which requires larger organizations’ public websites to meet WCAG 2.0 Level AA.
Class action: A lawsuit brought by one or more people on behalf of a larger group who met the same barrier.
Demand letter: A letter from a lawyer saying a client met a barrier on your website and asking you to fix it and settle before a lawsuit.
Disability Discrimination Act: Australia’s federal law making it unlawful to discriminate because of disability when providing goods, services, or facilities.
Equality Act 2010: The UK law that bars service providers from discriminating because of disability and requires reasonable adjustments.
European Accessibility Act: The EU law that requires covered products and services sold to consumers, including e-commerce and banking, to be accessible.
Public Sector Bodies Accessibility Regulations: The 2018 UK regulations requiring public sector websites and apps to meet WCAG 2.2 AA and publish an accessibility statement.
Section 504: The U.S. law covering organizations that receive federal money, with a health rule naming WCAG 2.1 AA for websites and apps.
Section 508: The U.S. law requiring federal agencies, and the technology they buy, to be accessible to people with disabilities.
Web Accessibility Directive: The EU law requiring public sector websites and apps to be accessible, with a statement and a way to report problems.

Testing and documentation

Accessibility evaluation: A structured review of how a website or app does against WCAG, done by people using assistive technology, not only a scan.
Accessibility overlay: A third-party script added to a website that claims to fix its accessibility automatically, which it cannot do.
Accessibility statement: A public page that says what standard you aim for, what is not yet accessible, and how to report a barrier.
ACR: An Accessibility Conformance Report, a completed VPAT that says how a specific product does against the standard.
Assistive technology testing: Testing a product with the actual tools people use, such as a screen reader, magnifier, switch, or voice control.
Automated testing: Software that scans a page for accessibility failures it can detect, such as missing alt text or low contrast.
Manual testing: A person checking a page by hand, with a keyboard, a screen reader, zoom, and judgment, for what tools cannot catch.
Monitoring: Ongoing checks that catch new accessibility barriers as a website or app changes.
Remediation: Fixing the barriers an evaluation found, usually in order of how badly each one blocks people.
Severity: How badly a barrier affects people, from stopping a task entirely to a minor inconvenience, used to order fixes.
Usability testing with people with disabilities: Watching people with disabilities use your product for real tasks, to find what a checklist and an expert miss.
VPAT: The standard template vendors fill in to report how a product does against accessibility standards.
WCAG-EM: The W3C’s step-by-step methodology for evaluating how well a whole website conforms to WCAG.

Design and process

Accessible by default: Setting up tools, templates, and components so that the quickest way to build something produces accessible results without extra effort.
Curb-cut effect: The pattern where a change made for people with disabilities ends up helping almost everyone.
Definition of done: A team’s checklist for when a piece of work is finished, which needs to include accessibility.
Design system: A shared set of components, colors, type, and rules that a team builds products from, where accessibility can be set once.
Inclusive design: Designing with the full range of human diversity in mind, so that solving for one person extends to many.
Progressive enhancement: Building a page so the basic HTML works first, then adding styling and scripts as improvements on top.
Shift left: Moving accessibility work earlier in a project, into design and development, instead of fixing it after launch.
Universal design: Designing products and places so that as many people as possible can use them without adaptation.