Web accessibility glossary
Find clear and concise definitions of essential digital accessibility terms: WCAG, RGAA, ARIA, WAI and many others.
A
- Accessibility Tree Shaking
- Accessibility tree shaking refers to the risk that code optimization tools (webpack, Vite, PurgeCSS) unintentionally remove code necessary for assistive technologies. The .sr-only class, focus management utilities, aria-live announcements: this code invisible on screen can disappear in production without anyone noticing visually.
- Accessible Name
- The accessible name is the text that assistive technologies use to identify an interface element. The browser calculates it according to a W3C algorithm by consulting multiple sources in a strict priority order: aria-labelledby, aria-label, HTML
<label>, text content, and finally the title attribute as a last resort. - Accessible Version
- An accessible version is a copy of a web page that complies with WCAG, offered as a replacement for a page that does not. It must provide the same information and functionality as the original, be kept up to date, and be directly reachable from the non-conforming page.
- Alt Attribute
- The alt attribute is the HTML attribute of the
<img>tag that contains the alternative text of an image. Screen readers read this text in place of the image, and browsers display it when the image fails to load. Three possible states: absent, empty, or filled — each produces different behavior. - Alternative Content
- Alternative content is an equivalent that replaces non-textual content to make it perceivable by everyone. The alt attribute on an image is its most well-known form, but the concept also covers captions, text transcriptions, and audio descriptions. WCAG makes it their very first principle.
- Alternative text
- Alternative text is the text that a screen reader reads instead of an image. In HTML, it's the alt attribute on images. Its content depends on the image's role on the page: informative, decorative, or functional.
- Alternative version
- An alternative version is content offered in a different format than the original to convey the same information in an accessible way. A scanned PDF replaced by an HTML document, a complex chart accompanied by a data table, a video dubbed with a transcript: each alternative version must be complete, up-to-date, and reachable.
- ARIA
- ARIA (Accessible Rich Internet Applications) is a set of HTML attributes that describe interface components to assistive technologies. A custom button, a tabbed system, a dynamic notification: when semantic HTML is not enough, ARIA adds the missing information. But an ARIA attribute without the corresponding behavior does more harm than good.
- ARIA Role
- An ARIA role tells assistive technologies what an interface element is: a button, tab, alert, navigation region. Semantic HTML tags already carry an implicit role. The role attribute is only necessary for components absent from native HTML, such as tabs or dropdown menus.
- Assistive Technologies
- Assistive technologies are the software and hardware that people with disabilities use to navigate the web: screen readers, magnifiers, voice commands, braille displays, switches. They depend entirely on the quality of the HTML code to function correctly.
C
- CAPTCHA
- A CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is a security test that distinguishes humans from robots on a website. The problem: most CAPTCHAs rely on vision or hearing, which excludes blind, visually impaired, or cognitively disabled people. Invisible alternatives exist.
- Change of Context
- In web accessibility, a change of context designates a major upheaval of the page: opening a new window, moving focus, redirecting to another page or significant reorganization of content. WCAG requires that these changes never occur automatically, unless the user triggered them or was notified in advance.
- Compatible with Assistive Technologies
- Web content is compatible with assistive technologies when the browser correctly transmits its information (name, role, value, states) to screen readers, braille displays, and other assistive tools. Native HTML elements like
<button>or<input>are automatically compatible. Generic elements like<div>are not, unless manual addition of WAI-ARIA attributes and keyboard behaviors. - Complex data table
- A complex data table is an HTML table whose headers do not cover an entire row or column, typically due to merged cells or sub-groups of headers. The scope attribute is no longer sufficient: each cell must be associated with its headers via id and headers attributes. When possible, splitting the table into several simple tables remains the best solution.
- Complex gestures and simple gestures
- A simple gesture is a single point of contact on the screen: click, double-click, long press. A complex gesture involves multiple fingers simultaneously (pinch to zoom) or follows a precise trajectory (swipe). WCAG requires that any functionality triggered by a complex gesture be equally accessible via a simple gesture.
- Composite Link
- A composite link groups an image and text within a single
<a>tag. The browser calculates the link's accessible name by concatenating the image's alternative text and the visible text. When the image and text are split into two separate links, screen readers announce two identical consecutive links. - Contrast
- Contrast measures the difference in brightness between two colors, expressed as a ratio from 1:1 to 21:1. In web accessibility, WCAG requires a minimum ratio of 4.5:1 for regular text and 3:1 for large text and interface components. Insufficient contrast is the most widespread accessibility error on the web.
- Contrast Ratio
- The contrast ratio is a number between 1:1 and 21:1 that measures the brightness difference between two colors. WCAG relies on this ratio to set readability thresholds: 4.5:1 for normal text, 3:1 for large text and interface components. It is calculated from the relative luminance of the two colors being compared.
- Controlled Environment
- A controlled environment refers to a context where an organization controls its users' workstations: operating system, browser, installed assistive technology. This applies to intranets, business applications, and partner extranets. When equipment is known, accessibility audits target this actual configuration instead of following the RGAA's default test combinations.
D
- Data Table
- A data table is an HTML element that organizes information in rows and columns, where each cell maintains a logical relationship with its headers. Unlike a layout table (used to arrange elements visually), a data table requires semantic markup (tags
<th>, scope attribute,<caption>element) so that screen readers convey the context of each value. - Decorative Image
- A decorative image is an image that provides no information to the page content. In HTML, it receives an empty alt attribute (alt="") so screen readers ignore it. Without this attribute, the screen reader reads the filename instead.
- Default language
- The default language of a web page is the primary language in which its content is written. It is declared in HTML with the lang attribute on the document's root element. Without this declaration, screen readers do not know which pronunciation rules to apply and read the text with the accent of the language configured on the user's system.
- Design Pattern
- A design pattern is a documented model that describes how to build an accessible rich interface component. It specifies the ARIA roles to use, the states to manage, and the keyboard interactions to code. The W3C publishes about thirty in the APG (Authoring Practices Guide), covering tabs, modals, application menus, and accordions.
- Detailed Description
- A detailed description is a long text that complements the alt text of a complex image (chart, diagram, map). When a single sentence is not enough to convey the information carried by a visual, the detailed description provides the complete textual equivalent, in the form of paragraphs, lists, or data tables.
- Disability Situation
- A disability situation is not a characteristic of the person. It is the result of the interaction between an individual's capacity and an environment that creates obstacles. A website without text alternatives puts a blind user in a disability situation; the same website, made accessible, eliminates this situation.
- Document structure
- Document structure is the logical organization of a web page through hierarchical headings (h1 to h6) and semantic HTML5 tags. Screen readers use them to build a navigable table of contents and allow their users to jump directly to the desired section.
E
- European Accessibility Act
- The European Accessibility Act (EAA) is a European Union directive that imposes common accessibility requirements for certain digital products and services. Adopted in 2019, it has been applicable since June 28, 2025 in all Member States.
F
- Focus
- Focus refers to the state of a web page element when it receives keyboard attention. A visual indicator, often an outline, signals which element is active. Without this indicator, keyboard navigation becomes impossible.
- Form
- A form is a set of fields and buttons that allow a user to transmit data on a website. To be accessible, each field must have a label linked in the code, related controls must be grouped in a fieldset, and errors must be reported as text. WCAG dedicates 13 criteria to it, its most comprehensive topic.
- Form Field Grouping
- Form field grouping consists of associating related controls in HTML code using fieldset and legend elements. This semantic grouping allows screen readers to announce the common context of the fields (for example, "Delivery Address") before each field in the group. Without it, identical labels like "First Name" or "Postal Code" become ambiguous.
- Form Field Label
- A form field label is the text that indicates the data expected by an input field ('Name', 'Email', 'Password'). To be accessible, this text must be linked to the field in HTML code via the label element or ARIA attributes. Without this link, screen readers announce a silent field with no indication of what to enter.
- Form Input Field
- A form input field is the HTML element in which a user enters or selects data: free text, date, checkbox, dropdown, file upload. To be accessible, each field must be linked in the code to a label that identifies the expected data. Without this connection, screen readers announce a silent field.
G
- Graphic element
- A graphic element is any non-textual visual content: image, SVG icon, pictogram, data chart. The term goes beyond the simple
<img>tag and also covers<svg>,<canvas>and<object>. Every graphic element that conveys information must have a text alternative; every decorative element must be hidden from assistive technologies.
H
- HTML Semantics
- HTML semantics means choosing HTML elements according to their meaning, not their appearance. A
<nav>tells browsers and screen readers "this is a navigation", whereas a<div>conveys no information. It's the foundation of code-side accessibility: well-structured HTML makes content understandable without JavaScript or extra ARIA attributes.
I
- Image link
- An image link is a link whose only clickable content is an image. Its text alternative (the alt attribute) becomes the link label for screen reader users. If the alt is missing or describes appearance instead of destination, the link becomes unusable.
- Image text
- An image text is an image whose visible content is text. Instead of using real HTML text styled with CSS, the text is flattened into an image file (PNG, JPG…). Users can then neither resize it, change the font, nor read it with a screen reader.
- Information Presentation
- Information presentation refers to the way content is visually formatted on a web page: colors, fonts, spacing, positioning. In accessibility, the principle is strict: all formatting is done through CSS, never through misused HTML tags. Content must remain understandable when styles are disabled or modified by the user.
- Information provided by color
- Information provided by color refers to any situation where a color difference is the only means of conveying meaning in a web interface. A field in red to signal an error, an underlined link, a chart without labels: all cases where color-blind people lose the information. WCAG criterion 1.4.1 (level A) and RGAA criterion 3.1 require always doubling the color with another visual indicator.
- Information-carrying image
- An information-carrying image is an image whose removal would cause a loss of meaning to the page. It conveys content that the surrounding text does not provide. The RGAA and WCAG require that it carries a text alternative describing the information conveyed, not the appearance of the image.
- Inline frame
- An inline frame (iframe in HTML) embeds a web page inside another page. YouTube videos, Google Maps, booking widgets: all use iframes. For accessibility, each inline frame must have a title attribute that describes its content, so screen readers can identify it.
- Inline frame title
- The inline frame title is the accessible name of an
<iframe>element, conveyed via the title, aria-label, or aria-labelledby attribute. This is the text that screen readers announce to identify the content of an embedded frame. RGAA dedicates two criteria to it: the frame must have a title (2.1), and that title must accurately describe the actual frame content (2.2). - Input Validation
- Input validation encompasses the mechanisms that help users fill out a form without errors: indicating required fields, specifying the expected format, and providing explicit error messages when input fails. Without these indicators, a screen reader user doesn't know what to fill in or what went wrong.
K
- Keyboard Accessible and Activatable
- A component is « keyboard accessible » when you can select it with Tab, and « activatable » when you can trigger its action with Enter or Space. Native HTML elements like
<a>,<button>and<input>are by default. A<div>with an onclick, is not. - Keyboard Shortcut
- A keyboard shortcut is a key or combination of keys that triggers an action without using the mouse. In web accessibility, poorly designed shortcuts create more problems than they solve: they conflict with screen readers and cause unintended actions for voice command users.
- Keyboard Trap
- A keyboard trap occurs when focus enters a component on the page and can no longer exit using standard keys (Tab, Escape, arrows). The user is stuck: impossible to continue without a mouse. WCAG criterion 2.1.2 (level A) prohibits this situation.
L
- Landmark Region
- In RGAA terminology, a landmark region designates a large structural section of a web page: header, navigation, main content, footer. It must be marked up with a semantic HTML5 element so that screen readers can offer direct access to each section.
- Landmarks
- Landmarks are structural markers that divide a web page into large regions: header, navigation, main content, footer. Screen readers use them to offer direct navigation to each section, without having to read through all HTML sequentially.
- Language Change
- A language change is a word or passage written in a language different from the main language of the page. In HTML, it is marked with the lang attribute on the element containing this text. Without this markup, screen readers pronounce the foreign text with the accent of the main language.
- Layout Table
- A layout table is an HTML
<table>element misused for visual positioning of elements on a page. It contains no logical relationship between rows and columns. To prevent screen readers from announcing it as a real table, it must carry the attribute role="presentation" or role="none" and contain no semantic data table tags (<th>,<caption>, scope). - Legend
- In web accessibility, a legend is visible text that identifies grouped content. HTML offers three tags depending on context:
<caption>for tables,<figcaption>for figures, and<legend>for field groups in a form. - Link context
- Link context is the HTML element that surrounds a link and makes its destination clear when the link text alone is insufficient. A paragraph, list item, table cell, or section heading can serve as context, provided that assistive technologies can read them.
- Link Purpose
- Link purpose is the text that assistive technologies announce to describe a link. In HTML, it corresponds to the text content of the link, the alt attribute of a linked image, or the value of aria-label. A vague purpose like 'click here' makes the link unusable outside a visual context.
N
- Non-temporal media
- Non-temporal media is multimedia content that users consume at their own pace, without an imposed chronological flow: interactive map, clickable chart, user-controlled slideshow. In accessibility, each non-temporal media must offer an accessible alternative and an adjacent, clearly identifiable link to it.
P
- Page Title
- The page title is the content of the HTML
<title>tag, displayed in the browser tab. It is the first information a screen reader announces when opening a page. WCAG criterion 2.4.2 (level A) requires that each page has a title describing its subject or function. - Presentation only
- The phrase "presentation only" describes two related realities in web accessibility. On the HTML side, it's the misuse of a tag to achieve a visual effect (a
<blockquote>to indent, an<h2>to enlarge text). On the ARIA side, it's the role="presentation" role (synonym role="none") that removes the semantics of an element from the accessibility tree while keeping its content visible.
R
- Rapid brightness changes or flashing effects
- A flash in web accessibility refers to a rapid and intense change in brightness between two opposite visual states. When this type of flickering exceeds 3 occurrences per second and crosses certain intensity thresholds, it can trigger photosensitive epilepsy seizures. WCAG standards impose strict limits to protect users.
- Reading Order
- Reading order is the sequence in which assistive technologies traverse the content of a web page. This sequence follows the HTML source code (the DOM), not the visual layout. When CSS rearranges elements on screen, the reading order can diverge from what the user sees.
- Responsive Image
- A responsive image is an HTML image divided into clickable areas, each leading to a different link. It relies on map and area tags associated with an img via the usemap attribute. RGAA requires text alternatives on the image and on each active area.
S
- Screen reader
- A screen reader is software that converts screen content into speech synthesis or braille. It traverses the browser's accessibility tree, not the design, to convey page structure to blind or low-vision users.
- Select list
- A select list is a form element that offers a menu of predefined options; in HTML it's the select element. The user opens the list, browses the options, and selects one or more. For assistive technologies, it's one of the most reliable native components, provided you don't replace it with a fake custom menu in divs.
- Set of Web Pages
- A set of web pages refers to a group of web pages that share a common objective and are produced by the same team. This concept, drawn from the WCAG glossary, defines the scope within which consistency rules in accessibility apply: same navigation, same labels, same help location.
- Site Map
- A site map is an HTML page that lists all the links on a website, organized by sections. It provides an overview of the site structure and serves as an alternative navigation method. Users who struggle to navigate through traditional menus find direct access to each page.
- Skip links
- Skip links are links placed at the very beginning of a page that allow keyboard users to jump directly to the main content without tabbing through the navigation menu. Hidden by default, they appear on keyboard focus. WCAG 2.4.1 (Level A) requires them on every page with repetitive blocks.
- Status Message
- A status message is information that appears on a page without moving the user's focus: send confirmation, form error, cart update. Sighted users spot it visually, but screen readers detect it only if marked with role="status" or an ARIA live region. WCAG criterion 4.1.3 (level AA) makes this signaling mandatory.
- Style Sheet
- A style sheet is a CSS file that defines the visual appearance of a web page. In accessibility, three origins coexist: the browser's, the developer's, and the user's. The RGAA verifies that informative content remains readable when author styles are disabled.
- Synchronized Audio Description
- Synchronized audio description is a voice narration inserted during pauses in a video to describe visual elements that the soundtrack does not convey. It enables people who are blind or visually impaired to follow the action, scene changes, and on-screen text. WCAG requires it at level AA for all prerecorded video content.
- Synchronized Audio Description
- Synchronized captions are a text version of the dialogue and sounds of a video, displayed in real time in the player. They are not limited to dialogue: they identify who is speaking and describe significant sounds such as music or a door slam. WCAG requires them at Level A for pre-recorded videos (criterion 1.2.2).
T
- Tab order
- Tab order is the sequence in which interactive elements on a page receive focus when the Tab key is pressed. By default, it follows the order of the HTML code. If this order does not match the visual order of the page, keyboard users become disoriented.
- Tabindex
- The HTML tabindex attribute controls whether an element can receive keyboard focus and in what order. Three values exist: 0 to include an element in the natural tab order, -1 to make it focusable only via JavaScript, and positive values, which you should never use.
- Table column or row header
- In a data table, a column or row header is the cell that serves as a title for the other cells in that column or row. In HTML, it's the
<th>tag that fulfills this role. Without it, a screen reader restores cells without context: the user hears values without knowing what they correspond to. - Text passage
- A text passage, in the RGAA glossary, refers to text present in a page's source code and referenced by another element via aria-labelledby or aria-describedby. It is the mechanism that allows a component to borrow its accessible name (or description) from text located elsewhere in the DOM.
- Time-based media
- Time-based media is content whose understanding depends on time flowing: audio file, video, or both combined. In accessibility, each type of time-based media requires specific alternatives: transcription, captions, audio description. WCAG devotes nine success criteria to it (guideline 1.2).
- Transcript
- A transcript is the written version of audio or video content, accessible independently from the player. It reproduces the spoken words, identifies speakers, describes significant sounds, and for videos, the visual information necessary for understanding. WCAG requires it from level A for all prerecorded audio-only content (criterion 1.2.1).
U
- UI Component
- A UI component is a page element with which the user interacts: button, link, input field, menu, or tab system. When it's a native HTML element, the browser handles accessibility. When built in JavaScript, it's the developer's responsibility to reproduce that behavior with WAI-ARIA and keyboard management.
W
- WAI-ARIA
- WAI-ARIA (Web Accessibility Initiative – Accessible Rich Internet Applications) is a W3C specification that adds semantic attributes to HTML: roles, states, and properties. These attributes enable assistive technologies to understand dynamic interface components that native HTML alone cannot describe. Version 1.2 is the official recommendation since June 2023.
- WAI-ARIA Role
- A WAI-ARIA role is an HTML attribute that tells assistive technologies the nature of an element: button, tab, alert, navigation region. Semantic HTML elements already carry an implicit role. A
<button>is announced as a button without configuration. ARIA roles are only needed when native HTML cannot express the desired semantics. - WCAG
- WCAG (Web Content Accessibility Guidelines) are the W3C recommendations that define how to make a website usable by everyone, including people with disabilities. Most legislation worldwide, including RGAA in France, relies on WCAG level AA as a compliance requirement.