📖 Glossary
102 words you will meet across accessibility work, from alt text and ARIA through to cross slope and clear opening. Each one gets a short definition, a real example, and a link to the page that explains it properly. Search it, or jump to a letter.
The idea that ability is not a yes or no. Everyone sits somewhere on a range for sight, hearing, movement, speech and thinking, and everyone moves along it during their life.
In practice One person is blind, another has cataracts, another left their reading glasses at home. All three benefit from text that scales.
Designing and building things so that disabled people can use them, on their own, without having to ask for help. The short form a11y is just the word accessibility with the eleven middle letters replaced by the number.
In practice A website works with a keyboard alone. A shop has a ramp as well as a step. Both are accessibility.
The stripped down version of a page that the browser hands to assistive technology. It holds each element's name, role, state and value, and nothing about colour or position.
In practice If a control is missing from the accessibility tree, or is in it with no name, a screen reader user cannot use it, however good it looks.
The text a screen reader announces for a control or an image. It comes from the visible label where there is one, and from alt text, aria-label or aria-labelledby where there is not.
In practice A button containing only a bell icon has no accessible name until you add one, so it is read as just "button".
A continuous path someone can travel without meeting a step, a narrow point or a steep slope. Continuous is the important word.
In practice A perfect ramp that ends at a narrow inward opening door has not created an accessible route. It has moved the barrier two metres.
The United States civil rights law covering disability, from 1990. It does not contain web measurements, which is why courts lean on WCAG.
In practice Its built environment rules, the ADA Standards for Accessible Design, are where a lot of the worked numbers in ramp guidance come from.
A short written description of an image, for people who cannot see it. Describe what the image is doing in the page, not every detail in it.
In practice alt="Our five person team outside the office" tells you something. alt="image" and alt="photo-final-v2.jpg" tell you nothing.
A set of extra HTML attributes that describe roles, states and properties to assistive technology. It changes what a control is announced as, never what it does.
In practice role="tablist", aria-expanded="false", aria-label="Close". Use it only when native HTML has no element for what you are building.
Any tool that helps a disabled person do something they could not otherwise do, or could not do comfortably.
In practice Screen readers, screen magnifiers, braille displays, switch devices, voice control, hearing aids, wheelchairs and reachers are all assistive technology.
The standard for the tools people make content with. It asks two things. The tool itself must be usable, and it must help the author produce accessible output.
In practice A content management system that will not let you publish an image until you have written alt text is following ATAG.
A spoken track that describes what is happening on screen, for people who cannot see it. It fills the gaps where the picture carries meaning the dialogue does not.
In practice "She slides the envelope under the door and walks away." Without it, a blind viewer just hears footsteps.
Software that scans a page for accessibility problems. Fast, free, and it finds roughly a third of what is actually there.
In practice It will catch a missing alt attribute. It cannot tell you the alt text is wrong.
Media that starts on its own when a page loads. It talks over a screen reader, it eats data, and it can trigger nausea or seizures where there is motion.
In practice The two limits are different, and people mix them up. Sound that starts on its own needs a control once it runs past three seconds, which is WCAG 1.4.2. Anything moving, blinking or scrolling gets five seconds, which is WCAG 2.2.2. Put the pause control early in the tab order either way.
A widely used automated accessibility checker, available as a browser extension and as a library you can run in tests.
In practice Run it on every page as a first pass, then do the keyboard and screen reader checks it cannot do.
Anything in a product or a place that stops someone getting through. The word matters because it puts the problem in the design rather than in the person.
In practice A step, a form field with no label, a video with no captions, a PDF that is a photograph of text.
The view that disability comes from three things interacting at once. The biological, meaning the body. The psychological, meaning how a person thinks and feels about their situation. And the social, meaning the environment and the people in it.
In practice It is the model behind the World Health Organization's ICF, and the official middle ground between the medical and social models.
A device with a row of pins that rise and fall to form braille, driven by the same output as a screen reader. Deafblind users often rely on it entirely.
In practice It reads exactly what the accessibility tree says, so a button with no name is blank on the display too.
The British standard for designing buildings and their approaches so disabled people can use them. It explains the reasoning behind the numbers, which makes it good for learning.
In practice Read ISO 21542 for the international requirement and BS 8300 for why the requirement is what it is.
Writing a hashtag with a capital at the start of each word, so assistive technology can find the word boundaries.
In practice #DisabilityPride is read as two words. #disabilitypride is read as one long noise, and #DISABILITYPRIDE may be spelled out letter by letter.
On screen text carrying everything you would hear, which means the dialogue plus the sounds that matter. Subtitles usually carry the dialogue alone.
In practice "[door slams] I told you not to come back." The slam is part of the story, so it belongs in the captions.
The view that disabled people are unfortunate and deserve pity and help from those more fortunate. It makes access a gift rather than a right, and a gift can always be withdrawn.
In practice The telethon. The word "brave" applied to somebody doing the shopping. Watch for it sneaking into campaigns nobody meant to be patronising.
The gap a person actually passes through, measured with the door open to 90 degrees, from the face of the leaf across to the stop on the other side.
In practice It is always less than the nominal door size, because the leaf, the hardware and the stop all eat into it.
The usable width of a route or a ramp, measured at its narrowest point, between whatever actually gets in the way.
In practice Measure between the handrails or the kerbs, not between the outer edges of the structure.
Using colour as the only way of telling something apart. It fails for colour blind users, in bright sun, on a cheap projector and in print.
In practice A red border on an invalid field is fine, as long as there is also an icon or a message saying what is wrong.
A text field joined to a list of suggestions. It is one of the easiest components to get wrong, because focus stays in the field while the highlight moves in the list.
In practice The pattern uses aria-activedescendant so the field keeps focus and the screen reader still announces the highlighted option.
How far up WCAG you are claiming to reach. Level A is the floor, AA is what nearly every law and contract asks for, AAA is not expected across a whole site.
In practice "WCAG 2.2 level AA" is the phrase to put in a contract. Asking for AAA everywhere is usually a sign nobody read the standard.
A number from 1 to 21 describing how far apart two colours are in lightness. Higher is easier to read.
In practice WCAG AA wants at least 4.5 to 1 for normal text, 3 to 1 for large text, and 3 to 1 for the parts of a control you need to see.
The slope across your direction of travel. It drags a wheelchair towards the low edge and forces constant correction.
In practice Usually capped around 1 in 48, which is about 2 percent. Turn the level sideways every time you measure.
What happens when something built for a specific disabled need turns out to help far more people than it was built for.
In practice Dropped kerbs were fought for by wheelchair users. Now they carry prams, delivery trolleys, suitcases and anyone with a bad knee.
An image that adds nothing a reader would miss. It should carry an empty alt attribute so assistive technology skips it.
In practice alt="" on a background swirl. Leaving the attribute off entirely is different, and makes some screen readers read the file name out loud.
Link text that still makes sense when it is read on its own, because screen reader users often pull up a list of all the links on a page.
In practice A page of nine links all called "read more" becomes a list of nine identical entries.
A button that shows or hides a chunk of content, with aria-expanded saying which state it is in. The simplest widget in the ARIA patterns, and the one most often built wrong.
In practice A "show the code" toggle. The button keeps focus, and the region below it appears.
European Union law requiring a set of products and services to be accessible, including e-commerce, banking, transport and ebooks. It applies to the private sector, not only to government.
In practice If you sell into the EU, this is the one that reaches your online shop.
The view that measures disability by its effect on the ability to work, and by what it costs the person, the employer and the state.
In practice Useful for opening a budget, dangerous as a justification. Lead with rights and follow with money, because a programme that exists only because it paid for itself gets cancelled the first year it does not.
A raised lip along the open edge of a ramp or a landing, commonly around 100mm, that stops a front castor dropping off the side.
In practice A castor going over the edge tips the chair forwards. This is a safety item, not a finish.
The European standard for accessible information and communication technology. It is what public bodies buy against.
In practice It does not compete with WCAG. Its web chapter contains WCAG, then adds hardware, documents and support services on top.
The standard for accessible ebooks, published as ISO/IEC 23761. It covers navigation, reading order, images and the metadata that lets a reader find out whether a book is usable before buying it.
In practice It is the ebook equivalent of PDF/UA, and it is a much better format to start from.
Telling someone which field is wrong and what to do about it, in text, near the field, and in a way a screen reader will announce.
In practice "Enter a date as day slash month slash year, for example 04/03/2026" beats a red outline with no words.
Something a tool flags that is not really a problem. The other half of the coin is the false negative, a real problem the tool never saw.
In practice This is why an automated score is a starting point rather than a result.
The place on a page where keyboard input will land. Exactly one thing has focus at a time, and Tab moves it.
In practice If you cannot tell what has focus, you cannot use a keyboard. That is why the focus indicator matters so much.
The visible outline showing what currently has focus. Removing it with outline: none and putting nothing back is one of the most common accessibility bugs there is.
In practice If the default ring clashes with the design, replace it with something clearly visible. Do not delete it.
The sequence Tab walks through. It follows the order of elements in the HTML, which is why moving things around with CSS can quietly break it.
In practice A menu that looks like it is at the top but sits at the bottom of the markup will be reached last.
Deliberately keeping focus inside a modal dialog so Tab cannot wander behind it. Done right it is essential. Done by accident it is a keyboard trap.
In practice Open a dialog, move focus into it, keep Tab cycling within it, and return focus to the button that opened it on close.
The practical view. There is a task the person cannot currently do, so find something that lets them do it. Deliberately uninterested in the politics.
In practice A portable ramp, a screen reader, a grab rail. All good things, and a portable ramp kept behind the counter still means somebody has to ask.
Slope written as rise to run. 1 in 12 means one unit up for every twelve along.
In practice 1:12 is 8.33 percent. 1:20 is 5 percent. Divide the rise by the run to get the decimal, then multiply by 100.
The outline formed by h1 to h6. Screen reader users jump between headings constantly, so the outline is a map rather than a set of font sizes.
In practice One h1 per page, then h2 for sections and h3 inside those. Never skip from h2 to h4 because h3 looked too big.
A way of working, rather than a result. You bring people who are usually left out into the design process itself, and you accept that one solution may not fit everyone.
In practice Running a usability session with three blind users before you write any code, rather than auditing the finished thing.
The international standard for accessibility of the built environment. Ramps, doors, circulation, sanitary rooms, evacuation and wayfinding.
In practice This is the first place to look for a building, a hotel or an office, alongside whatever the local building code enforces.
The international standard for tactile walking surface indicators, the textured paving that guides and warns blind and partially sighted people.
In practice The blistered surface at a crossing means stop. The bar shaped one along a route means follow this line.
The standard for embedding accessibility into how an organisation actually works, from policy and procurement through to maintenance.
In practice If your team keeps shipping accessible pages and breaking them a month later, that is a process problem, and this is the standard aimed at it.
Unplugging the mouse and using the page with Tab, Shift Tab, Enter, Space, the arrow keys and Escape.
In practice The cheapest and most revealing test there is. If you can do it, you can find most problems.
A place you can Tab into and cannot Tab out of. WCAG treats it as a failure on its own, because it can end the session for a keyboard user.
In practice An embedded player that swallows Tab, or a custom widget that keeps resetting focus to itself.
A level platform at the top, at the bottom and between flights of a ramp. Somewhere to stop, to open a door and to turn.
In practice Usually at least 1500mm long and genuinely level. A landing that slopes is not a landing.
A region of a page that assistive technology can jump straight to. Native elements provide them for free.
In practice header, nav, main, aside and footer give you banner, navigation, main, complementary and contentinfo without a single ARIA attribute.
The attribute that tells assistive technology which language to pronounce the text in. Set it on the html element, and again on any passage in another language.
In practice Without lang="en" a Dutch voice may read English text, which is close to unintelligible.
A doorway with no step, or a lip small enough that a wheelchair rolls over it without stopping.
In practice A 25mm lip does not sound like much. It stops a small front castor dead. The usual limit is 15mm at most, and anything over about 6mm wants a bevel rather than a square edge.
The audit tool built into Chrome DevTools. Its accessibility score is an automated check with the same limits as any other.
In practice A score of 100 means no automated failure was found. It does not mean the page is accessible.
A part of a page that announces its own changes, without moving focus. It is how you tell a screen reader user that something updated.
In practice aria-live="polite" on a results count, so "12 results" is spoken while the user keeps typing.
A person using the thing the way a disabled person would, with a keyboard, a screen reader, zoom, or all three.
In practice This is where you find the alt text that says "image", the heading order that makes no sense, and the focus that vanishes.
The older view that disability is a problem inside a person, which should be treated or corrected so they can fit the world as it is.
In practice "He cannot get in because he uses a wheelchair." The sentence blames the chair rather than the step.
A window that blocks the page behind it until you deal with it. It has to take focus, keep focus, close on Escape and hand focus back.
In practice The native dialog element with showModal gives you most of this behaviour without writing it yourself.
The set of lenses for answering one question: where is the problem? The accessibility profession teaches seven, disability studies has named around two dozen, and the answer each gives decides what work it asks you to do.
In practice Sort them by what they do to people. Some hold people back, some sit in the middle, and some push things forward. Where a model puts the problem is the whole argument.
Normative text is the part of a standard you have to meet. Informative text explains, suggests and gives examples, and you do not have to follow it.
In practice The WCAG success criteria are normative. The techniques and the understanding documents are informative.
How hard you have to push or pull a door. A strong closer defeats people with limited strength even where the door is wide enough.
In practice If you have to lean into it, note it. Width is not the only thing that makes a door usable.
The standard for a PDF that assistive technology can actually read, which means tagged structure, a proper reading order, real text rather than a picture of text, and alt text on images.
In practice WCAG was written for web content. When a supplier hands you a PDF, this is the standard to hold it to.
The grey hint inside an empty field. It is not a label. It disappears the moment someone types, and its contrast is usually too low to read.
In practice Keep the placeholder for an example of the format, and add a real label above the field.
Writing that the reader understands the first time. Short sentences, common words, one idea at a time, and the point at the start rather than the end.
In practice "Send us your form by 3 March" instead of "submissions must be received no later than the aforementioned date".
The four principles WCAG is organised under. Perceivable, Operable, Understandable, Robust.
In practice Perceivable means you can sense it. Operable means you can work it. Understandable means it makes sense. Robust means it survives different browsers and assistive technology.
The band of heights a seated person can comfortably operate a control in, usually taken as 400mm to 1200mm from the floor.
In practice Light switches, card readers, buttons and handles all live in this band, measured to the centre of the control.
A specific change made for one person, because the normal way of doing things does not work for them. It is a legal duty in most places, and it is individual rather than universal.
In practice Giving an employee screen reader software and a quiet desk. Universal design would have made the software accessible in the first place, so fewer people ever need to ask.
A system setting saying the person does not want animation. Honour it, because motion causes real nausea and migraine for some people.
In practice Wrap your transitions in a prefers-reduced-motion media query and cut them to nothing when it is set.
Content rearranging to fit a narrow window instead of forcing sideways scrolling. WCAG asks for it down to 320 pixels wide.
In practice Zoom a page to 400 percent. If you now have to scroll left and right to read a sentence, reflow has failed.
Rise is the vertical height a ramp gains. Run, sometimes called the going, is the horizontal distance it covers doing it.
In practice A 150mm rise at 1:12 needs 1.8m of run. The same rise at 1:20 needs 3m.
What a thing is, as far as assistive technology is concerned. Native elements have one already, and ARIA can add or override it.
In practice button, link, checkbox, dialog, tab. A div has no role at all until you give it one.
A pattern where a group of controls counts as one Tab stop, and the arrow keys move between the items inside it.
In practice A tab set. Tab reaches the tab list once, then Left and Right move between the tabs. That is how native widgets behave.
The slope along your direction of travel. This is the number people mean when they say a ramp is 1 in 12.
In practice Take three readings and report the worst one. A user has to negotiate the steepest point, not the average.
Software that enlarges part of the screen, so the user sees a small window of a much bigger page at any moment.
In practice Content that appears far from what triggered it, like a message at the top of a long form, may never be seen.
Software that reads a screen aloud, or sends it to a braille display, and lets the user navigate by headings, links, landmarks and form fields.
In practice NVDA and JAWS on Windows, VoiceOver on Mac and iPhone, TalkBack on Android. NVDA and VoiceOver cost nothing.
The United States rule requiring federal agencies to buy and build accessible technology. It points at WCAG for the technical detail.
In practice This is why a supplier selling to a US agency is asked for a conformance report.
Using the element that means the thing, rather than a div with a class name that describes it. You get keyboard support, roles and states for free.
In practice button, not div class="btn". nav, not div class="nav". The class name is invisible to assistive technology.
A barrier that comes from where you are rather than from your body, and which comes and goes.
In practice Watching a video on a bus with no headphones. Reading a screen in bright sun. Holding a baby, so you have one hand.
A link at the very top of a page that jumps past the navigation to the main content. It is usually hidden until it takes focus.
In practice Without it, a keyboard user Tabs through the same forty menu links on every single page.
The view that disability is also something people share, with a community, a history, a culture and sometimes a language of its own.
In practice Deaf culture, written with a capital D. Many Deaf people do not consider themselves disabled at all, but a linguistic minority with their own sign language and schools.
The view that people have impairments, and that disability is created by an environment which fails to account for them. It moves the fix from the person to the design.
In practice "He cannot get in because there is a step and no ramp." Now there is something you can actually build.
The changeable facts about a control. A state can flip, a property normally does not.
In practice aria-expanded and aria-checked are states. aria-label and aria-labelledby are properties.
One testable requirement in WCAG, with a number and a level. There are 86 of them in WCAG 2.2 across the three levels. You will still see 87 quoted, because 4.1.1 Parsing was removed in 2.2 and older reports have not caught up.
In practice 1.1.1 Non-text Content is level A. 1.4.3 Contrast (Minimum) is level AA.
Operating a device with one or two large buttons, often by head, hand or breath, with the software scanning through the options.
In practice Every extra control on a page costs a switch user real time, so a short focus order is a kindness.
The attribute controlling whether an element can take focus. Only three values are worth using.
In practice tabindex="0" puts a custom element in the normal order. tabindex="-1" makes it focusable by script only. A positive number breaks the order and should be avoided.
Textured ground surfaces that a blind or partially sighted person can feel through a shoe or a cane.
In practice Blisters warn of a hazard such as a crossing. Bars guide you along a route. Getting the two the wrong way round is worse than laying none.
A documented way of meeting a success criterion. Techniques are advice rather than obligation, and there is usually more than one way through.
In practice You do not have to use a listed technique. You do have to meet the criterion.
The area you can actually tap. Small targets fail for large fingers, for tremor and for anyone on a moving bus.
In practice WCAG 2.2 asks for at least 24 by 24 pixels. Around 44 by 44 is a much more comfortable working target.
The full text of an audio or video piece, as a page you can read, search and translate. For anything speech only it matters more than captions.
In practice A podcast with a transcript can be read by a Deaf user, skimmed by a busy one and found by a search engine.
The clear space a wheelchair needs to turn around, usually taken as a 1500mm circle, or a T shape where a full circle will not fit.
In practice If a bin, a planter or a door swing intrudes into the shape, the space does not count.
The standard for browsers and media players themselves. Mostly relevant to the people who build them, but worth knowing exists.
In practice It is why your browser has zoom, caption controls and keyboard access to everything in its own interface.
The United Nations treaty that creates the right. Countries sign it and then write their own laws to deliver it.
In practice Article 9 covers accessibility and Article 21 covers access to information. These are the two to quote when making the case to a board.
Designing something so that as many people as possible can use it, from the start, with no adaptation and no separate version.
In practice A step free entrance that everybody uses, rather than a main staircase plus a lift around the back by the bins.
Driving a device by speaking. The user says the visible label, so the visible label and the accessible name need to match.
In practice A button that reads "Submit" but is labelled "Send form" in ARIA cannot be triggered by saying either one reliably.
A document in which a supplier states, criterion by criterion, how accessible their product is. The VPAT is the blank template and the ACR is the filled in result.
In practice Read the remarks column rather than the headline. "Supports" with a paragraph of exceptions underneath is not the same as supports.
A browser extension that draws its findings straight onto the page, which makes it easy to show a colleague what is wrong.
In practice Good for explaining a problem to someone who does not read code.
The main technical standard for digital accessibility, written by the W3C. Version 2.2 became the recommendation in October 2023, and an ISO standard, ISO/IEC 40500:2025, in October 2025.
In practice It is not a law by itself. Laws in many countries point at it, which is what gives it teeth.
European Union law requiring public sector websites and apps to be accessible, to publish an accessibility statement and to provide a feedback route.
In practice It is the public sector counterpart to the European Accessibility Act.
Enlarging a page in the browser. Very common, very cheap, and it breaks a surprising number of layouts.
In practice Test at 200 percent. Nothing should be cut off, overlapping or scrolling sideways.
Nothing matches that. Try a shorter word, or .
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