The words that come up in every audit.

A

Accessibility statement

A public page that names the standard a site aims to meet, lists known limitations, and explains how to report a barrier and get help. The European Accessibility Act requires service providers to publish information on how their services meet its requirements, and most do it this way. Ours is here.

Accessibility tree

The structure a browser derives from the DOM to describe each meaningful element by role, name, and state, exposed to assistive technology through the operating system's accessibility APIs. AI agents and test tools read it too. See The accessibility tree is your AI interface.

Accessible name

The text a browser exposes as an element's name, such as "Add to cart" for a button. It is computed from sources like aria-labelledby, aria-label, a <label>, alt text, or the element's own content, in a defined order. Screen readers announce it, voice control users speak it, and AI agents use it to decide what to click.

ACR (Accessibility Conformance Report)

A completed VPAT® that documents how a specific product version supports each accessibility criterion, with remarks explaining any gaps. Buyers use ACRs to compare products during procurement. See VPAT® & Accessibility Conformance Reports.

ADA Title II

The part of the Americans with Disabilities Act covering state and local governments, including public schools, universities, courts, libraries, and transit agencies. A Justice Department rule sets WCAG 2.1 Level AA as the technical standard for their websites and mobile apps. The dates are on our compliance deadlines page.

ADA Title III

The part of the ADA covering businesses open to the public, which the law calls public accommodations. There is no Title III regulation with a web standard, so demand letters, lawsuits, and settlements usually measure websites against WCAG 2.x Level AA.

AI agent

Software that uses a language model to carry out tasks on websites for a person, such as comparing products, booking appointments, or filling in forms. Agents perceive pages through screenshots, raw HTML, and the accessibility tree. See our Agent-Readiness Audit.

Alt text

The text alternative for an image, set in the alt attribute, that conveys what the image communicates in context. Informative images need a meaningful description; decorative images take an empty alt="" so screen readers skip them. Required by SC 1.1.1 Non-text Content.

ARIA

WAI-ARIA, the W3C specification for roles, states, and properties, such as role="dialog" or aria-expanded, that describe custom widgets to assistive technology. ARIA changes what is announced, not how anything behaves, which is why the first rule of ARIA is to use a native HTML element when one exists.

Assistive technology

Hardware or software people use to operate computers and phones in ways that suit them: screen readers, screen magnifiers, braille displays, switch devices, voice control, and alternative keyboards.

Audio description

Narration that describes important visual information in a video, such as actions, on-screen text, or scene changes, that the dialogue doesn't convey. SC 1.2.5 Audio Description (Prerecorded) requires it for prerecorded video at Level AA.

Automated accessibility testing

Tools such as axe-core and Lighthouse that check rendered pages for failures a machine can decide, like missing form labels or low contrast. They are fast and worth running on every build, but they can't judge meaning, such as whether alt text is accurate or a focus order makes sense. See What accessibility automation catches.

C

Captions

Synchronized text of the dialogue and important sounds in a video, for people who are deaf or hard of hearing. WCAG requires captions for prerecorded video at Level A (SC 1.2.2) and for live video at Level AA (SC 1.2.4).

Certificate transparency

A system of public, append-only logs that record the TLS certificates issued by publicly trusted certificate authorities. Searching the logs, for example with crt.sh, reveals hostnames an organization has secured, including ones it forgot. See Every organization has websites it forgot it owns.

CLS (Cumulative Layout Shift)

The Core Web Vital for visual stability. It scores how much visible content moves unexpectedly while a page is in use; 0.1 or less is good. Images without dimensions, late-loading ads, and injected banners are the usual causes.

Cognitive accessibility

Design that works for people with cognitive, learning, and neurological disabilities: plain language, consistent navigation, forgiving forms, and no unnecessary time limits. WCAG 2.2 added criteria in this area, including SC 3.3.7 Redundant Entry and SC 3.3.8 Accessible Authentication (Minimum).

Conformance level

WCAG's three tiers of success criteria: A, AA, and AAA. Laws and contracts almost always ask for Level AA, which means meeting every A and AA criterion. W3C does not recommend requiring AAA for entire sites, because some content can't meet every AAA criterion.

Consent management platform (CMP)

Software that shows a consent banner, records each visitor's choices, and tells tags whether they may run. It only controls the tags that are wired to it, so hard-coded pixels can slip past. See Tag & Script Governance.

Contrast ratio

A measure of the difference in luminance between text and its background, from 1:1 to 21:1. SC 1.4.3 Contrast (Minimum) requires at least 4.5:1 for normal text and 3:1 for large text at Level AA.

Core Web Vitals

Google's three field metrics for page experience: Largest Contentful Paint for loading, Interaction to Next Paint for responsiveness, and Cumulative Layout Shift for visual stability. Each is assessed at the 75th percentile of real page loads. See Core Web Vitals Engineering.

CrUX (Chrome UX Report)

Google's public dataset of field performance data from Chrome users who have opted in. It reports Core Web Vitals for sites and pages with enough traffic, and tools such as PageSpeed Insights and Search Console draw on it.

CSP (Content Security Policy)

An HTTP response header that tells the browser which sources of scripts, styles, frames, and connections a page may use. A strict CSP blocks unapproved scripts and doubles as a written list of the ones you did approve.

D

Data protection assessment

A documented review that weighs the benefits of a data processing activity against its risks to consumers. Laws like the KCDPA require one for activities such as targeted advertising, selling personal data, and processing sensitive data.

Demand letter

A letter, usually from a plaintiff's law firm, alleging that a website or app is inaccessible and proposing a settlement before a lawsuit is filed. The legal response belongs to your attorney; the technical review is where we help. See The first 72 hours after an ADA website demand letter.

Digital estate

Everything an organization publishes or controls online: domains, subdomains, microsites, apps, documents, and vendor-hosted pages that carry its name. See our Digital Estate Audit.

E

EAA (European Accessibility Act)

Directive (EU) 2019/882, which sets accessibility requirements for products and services sold to consumers in the EU, including e-commerce, consumer banking, e-books, and electronic communications. Each member state enforces it through national law. See One year in, the European Accessibility Act reaches US checkouts.

EN 301 549

The European standard for accessibility of ICT products and services. Its web and software clauses incorporate the WCAG 2.1 Level A and AA success criteria, and it adds requirements for hardware, two-way voice communication, video, documentation, and support services.

F

Field data

Performance measured from real visitors on their own devices and networks, as in CrUX or your own real user monitoring. Core Web Vitals assessments are based on field data, not lab tests.

Focus indicator

The visible outline or highlight that shows which element has keyboard focus. SC 2.4.7 Focus Visible requires one, and WCAG 2.2's SC 2.4.11 Focus Not Obscured (Minimum) means sticky headers and cookie banners can't completely cover it.

Focus order

The sequence in which interactive elements receive focus as someone presses Tab. SC 2.4.3 Focus Order requires a sequence that preserves meaning and operability, which usually means following the visual reading order.

Forced colors mode

An operating system setting, such as Windows contrast themes, that replaces a site's colors with a palette the user chooses. Anything that signals state only through a background color or background image can disappear; the CSS forced-colors media query lets you adjust.

H

HAR file

HTTP Archive: a JSON record of every network request a page made, exported from browser developer tools. Useful as evidence, and for comparing what loads before and after a visitor gives consent.

I

INP (Interaction to Next Paint)

The Core Web Vital for responsiveness. It measures how long a page takes to show a visual response after clicks, taps, and key presses, reported close to the slowest interaction of a visit; 200 milliseconds or less is good. See INP and accessibility share root causes.

J

JAWS

Job Access With Speech, a commercial screen reader for Windows that is widely used in workplaces.

K

KCDPA (Kentucky Consumer Data Protection Act)

Kentucky's consumer privacy law, codified at KRS 367.3611 to 367.3629. It gives Kentucky consumers rights over their personal data, including the right to opt out of targeted advertising, and the Attorney General enforces it. See our Kentucky privacy law checklist.

Keyboard trap

A component that keyboard focus can enter but not leave, such as a modal or embedded player with no way out. SC 2.1.2 No Keyboard Trap is Level A, because a trap stops a keyboard user completely.

L

Lab data

Performance measured in a controlled test, such as Lighthouse on a simulated mid-range phone. It's ideal for debugging and catching regressions, but it can't reproduce every device, network, and interaction your real visitors bring.

Landmark

A region of a page, such as banner, navigation, main, search, or contentinfo, that screen reader users can jump between. HTML elements like <header>, <nav>, <main>, and <footer> create landmarks automatically in most contexts.

LCP (Largest Contentful Paint)

The Core Web Vital for loading. It measures the time until the largest image or text block in the viewport renders; 2.5 seconds or less is good.

Lighthouse

Google's open-source lab tool for auditing performance, accessibility, SEO, and best practices, built into Chrome DevTools. Its accessibility score reflects automated checks only, so a perfect score is not the same as an accessible page.

Live region

An area marked with aria-live, or a role such as status or alert, whose updates screen readers announce without moving focus. Used for cart counts, form errors, and search result totals.

llms.txt

A proposed convention for a Markdown file at a site's root that gives language models a short summary of the site and links to its key content. It is a community proposal, not a web standard, and support among AI tools varies.

Long task

Any task that keeps the browser's main thread busy for more than 50 milliseconds. While it runs, the page can't respond to input, which makes long tasks a common cause of poor INP.

M

Main thread

The browser thread that runs most JavaScript, calculates styles and layout, and handles user input. When third-party scripts crowd it, clicks and key presses have to wait.

N

NVDA

NonVisual Desktop Access, a free, open-source screen reader for Windows.

O

Overlay

A third-party script or widget that tries to fix accessibility by altering a page after it loads, often with a toolbar of display options. Overlays don't change the underlying source code and can interfere with people's own assistive technology. See Overlays after the FTC order.

P

PDF/UA

PDF/Universal Accessibility, the ISO 14289 standard for accessible PDF files. PDF/UA-1 applies to PDF 1.7 files and PDF/UA-2 to PDF 2.0. See Document & PDF Accessibility.

Performance budget

A limit your team agrees not to exceed, such as total JavaScript weight, the number of third-party requests, or an LCP target, enforced in your build pipeline so pages don't slowly get heavier.

Pixel

A small piece of tracking code, originally a one-pixel image and now usually JavaScript, that reports page views and actions to an advertising or analytics platform.

Pre-consent firing

When a tag sends data or stores an identifier before a visitor makes a consent choice, or after they decline. See The pixel that fires before your visitor decides.

R

Reading order

The sequence in which assistive technology reads content. On a web page it follows the DOM; in a tagged PDF it follows the tag tree. When it differs from the visual order, a screen reader user hears a sidebar in the middle of a sentence.

Reduced motion

A user preference, exposed to CSS as prefers-reduced-motion, that asks for less animation. Respecting it helps people with vestibular disorders, for whom parallax and zoom effects can cause dizziness or nausea.

Reflow

SC 1.4.10 Reflow (Level AA): content must be usable at a width of 320 CSS pixels without scrolling in two directions. That is roughly what a desktop page looks like zoomed to four times its size.

Remediation

Fixing accessibility barriers at their source, in the HTML, CSS, JavaScript, design components, or document files, and then retesting. See Source-Code Remediation.

RUM (real user monitoring)

Collecting performance data from your own visitors' browsers with a small script, so you can break results down by page, device, and region. RUM gives you your own field data.

S

schema.org

A shared vocabulary for structured data, started by major search engines, that defines types such as Product, Organization, Event, and FAQPage and the properties each one can have.

Screen reader

Software that converts what's on screen into speech or braille and lets people navigate by headings, links, landmarks, and form controls. Common ones are JAWS, NVDA, VoiceOver, and TalkBack.

Section 504

Section 504 of the Rehabilitation Act bars disability discrimination in programs that receive federal financial assistance. Each funding agency writes its own rules; HHS's rule for its recipients sets WCAG 2.1 Level AA for web content and mobile apps. See the Title II and Section 504 extensions.

Section 508

Section 508 of the Rehabilitation Act requires federal agencies to make the information and communication technology they develop, buy, or use accessible. The revised 508 standards incorporate WCAG 2.0 Level AA, and vendors to federal agencies are often asked for a 508-edition ACR.

Semantic HTML

Using HTML elements for what they mean: <button> for actions, <a> for navigation, <label> for form labels, and headings for structure. Browsers turn semantics into roles and names in the accessibility tree without any extra code.

Server-side tagging

Sending analytics and marketing events to a server you control, which forwards them to vendors, instead of loading each vendor's script in the browser. It can lighten pages, but it moves data flows out of the browser's view, so consent has to be enforced on the server too.

Session replay

A script that records clicks, scrolls, and sometimes keystrokes so a visit can be played back later. Unless form fields are masked, it can capture personal data visitors type.

Skip link

A link at the very start of a page, often visible only when focused, that jumps past repeated navigation to the main content. It's the most common way to meet SC 2.4.1 Bypass Blocks.

Structured data

Machine-readable descriptions of what a page contains, usually written as JSON-LD with the schema.org vocabulary, such as a product's name, price, and availability. Search engines and AI agents use it, and it should always match what's visible on the page.

Subdomain takeover

When a DNS record still points at a third-party resource that no longer exists, such as a deleted cloud storage bucket, and an attacker claims that resource to serve content on your subdomain. Prevent it by removing DNS records before deprovisioning what they point to.

Success criterion

A single testable requirement in WCAG, such as SC 1.4.3 Contrast (Minimum) or SC 2.1.1 Keyboard. Each has a number, a name, and a conformance level. WCAG 2.2 has 55 success criteria at Levels A and AA.

T

Tag manager

A system that loads marketing and analytics tags through one container script and is configured in a web interface instead of code. It's convenient, and it's also the easiest way for an unreviewed script to reach production.

Tagged PDF

A PDF with a structure tree of tags, such as headings, paragraphs, lists, tables, and figures, that assistive technology reads instead of guessing from the visual layout. Tags are necessary for an accessible PDF, and they also have to be correct.

TalkBack

The screen reader built into Android.

Target size

The clickable or tappable area of a control. WCAG 2.2 SC 2.5.8 Target Size (Minimum) sets a minimum of 24 by 24 CSS pixels at Level AA, with exceptions for adequate spacing, inline links, and a few other cases.

Third-party script

JavaScript served from another company's domain, such as analytics, ads, chat, reviews, or A/B testing. Each one costs main-thread time and may collect visitor data. See The third-party script tax.

TTFB (Time to First Byte)

The time from the start of a navigation until the first byte of the response arrives. It isn't a Core Web Vital, but a slow server response delays everything after it, including LCP.

V

Voice control

Software that lets people operate a device by speaking, such as saying "click Add to cart." It works best when visible labels match accessible names, which is what SC 2.5.3 Label in Name requires.

VoiceOver

The screen reader built into Apple's macOS, iOS, and iPadOS.

VPAT®

The Voluntary Product Accessibility Template, published by the Information Technology Industry Council (ITI) in WCAG, Section 508, EU, and international editions. Once completed for a product, it becomes an Accessibility Conformance Report. VPAT is a registered service mark of ITI.

W

WCAG

The Web Content Accessibility Guidelines, published by the W3C. WCAG 2.2 is the current version; it organizes testable success criteria under principles and guidelines at Levels A, AA, and AAA. Most laws reference WCAG 2.0 or 2.1 Level AA.

WCAG 3.0

The next major version of WCAG, still a W3C Working Draft. Drafts propose a different structure, a different conformance model, and a broader scope, and W3C says it will not supersede WCAG 2. See Planning for WCAG 3 without the panic.

WebMCP

A proposed browser API that would let a web page expose structured tools, such as searching a catalog or adding an item to a cart, for AI agents to call directly. It is developed in a W3C Community Group and is not a W3C Standard.