A11Y - (pronounced "A - eleven - Y") - a "numeronym", or a number-based acronym, which uses the first and last letter from the word "accessibility" and inserts the number of letters found in between to form a convenient and easy-to-recognize abbreviation.

Accessibility (Web) - uses the principle of universal design to make websites, applications, and content usable by persons with or without disabilities who may or may not be using assistive technologies to access the site.

ADA (Americans with Disabilities Act) - a U.S. federal law that prohibits discrimination against people with disabilities in several areas, including employment, transportation, public accommodations, communications and access to state and local government programs and services.

Alt Text (also known as Alternative Tag, or Image Alt Tag)- provides text equivalents for non-text content, such a the short text that describes an image.

ARIA (Accessible Rich Internet Applications) - set of roles, states, and properties that are added as tags to HTML elements to describe the purpose of common interface elements that lack semantic HTML tags, such as notes, alerts, search bars, and menus, and enhance the accessibility of HTML for screen readers beyond what plain HTML can do.

Assistive Technologies - any device (item, piece of equipment, software, or system) used to increase, maintain, or improve the functional capabilities of a person with a disability, including screen readers, head and mouth wands, speech recognition software, adaptive keyboards, eye-tracking systems, and more.

Audio Browser -a web browser that provides a text-to-speech capability for the blind and visually impaired by using the HTML code from a web page to readily identify links, article headers, body text and other attributes to allow users to easily skip around the page.

Captions - text versions of the spoken words and important sounds presented within a video, which can either be presented as Closed (able to be turned on or off), or Open (are always visible).

Clickability cues - a visual indication, such as color, underlining, bullets, and arrows, that indicates a given word or item on a web page is clickable.

Color contrast (ratio) - a mathematical measurement expressed as a ratio, measuring the visual difference between background and foreground colors.

Curb cut effect - the phenomenon of disability-friendly features being used and appreciated by a larger group than the people they were originally designed for.

Focus, Focus Indicator - a solid or dotted border drawn around the place where the keyboard is currently located to serve as a visual indicator for the element that will respond to the next user action.

Hierarchy - the organization of web page content by level of importance, often established with HTML heading elements (< h 1 >, < h 2 >, < h 3 >, and so on), that helps screen reader users to understand the structure of a the web page and navigate efficiently.

Inclusive design - (see "Universal Design")

Nesting - refers to the hierarchy of headings in a page structure or a list of items, with one (1) first (1st) degree heading being the most important (for example, your site name or document title), followed by second (2nd) degree headings (for example, the major section headings of your document), then by third (3rd) degree headings (for example, subsections of the major section headings of your document), and so on.

POUR - (Perceivable, Operable, Understandable, and Robust) - the four main guiding, human-focused principles of accessibility, developed by WCAG.

Pseudo-class (CSS) (:) - primarily used to style an element that's under various states, which includes the condition or user behavior, and generally involves user interaction, such as :hover, :active, :focus, or :disabled.

Pseudo-element (CSS) (::) - used to style specific parts of an element, such as the ::first-letter or ::first-line of text, or to insert content ::before or ::after the element.

Screen reader - a software program that takes the on-screen text from a website or computer screen and reads it out loud for users with visual impairments, allowing for visual cues such as images, graphics or table headers to be perceived when additional information, such as image alt tags and specification of key landmarks are provided within the code of a given document.

Section 508 - an amendment to the U.S. Rehabilitation Act of 1973 introduced to "eliminate barriers in information technology, to make available new opportunities for people with disabilities, and to encourage the development of technologies that will help achieve these goals," and requires that information technology used or developed by a federal agency is fully accessible to people with disabilities.

Semantic HTML (or Semantic Markup) - the HTML code that communicates the meaning of its elements through the proper use of HTML tags, helping people using assistive technologies to better understand the structure and components of a web page.

SVG (Scalable Vector Graphics) - a web-friendly vector file format (".svg") written in XML code, that stores images via mathematical formulas based on points and lines on a grid, as opposed to pixel-based raster files like JPEGs.

Screen magnifier - a built-in device, or software program that makes images and text on a screen larger for the benefit of visually impaired users.

SEO (Search Engine Optimization) - the process used to optimize a website's technical configuration, content relevance and link popularity so its pages can become easily findable, more relevant and popular towards user search queries.

Switch Control/Access - an assistive technology that enables a person with limited mobility to interact with an iPhone or Android by activating a switch, such as pressing an external adaptive button, performing a head movement, or making a voiced or voiceless sound.

Tab order - an HTML attribute that defines the order in which the focus has to switch between the page elements when using a keyboard for navigation.

Title II - section of the ADA that prohibits disability-based discrimination on the part of state and local governments.

Title III - section of the ADA that details accessibility to public accommodations, stating that individuals with disabilities must be granted full and equal access to the benefits and programs provided by public accommodations, including not only physical addresses of these entities but to their websites as well.

Transcript - a written version of an entire video (like a screenplay) or audio file and should include descriptions of important sounds and visual elements, such as indications of laughter or an explosion.

Universal design - (also "Barrier-Free" or "Inclusive Design") - refers to the design of products and environments to be usable by all people, to the greatest extent possible, without the need for adaptation or specialized design.

Usability - measures how easily, effectively, and enjoyably a person uses and experiences a product. In terms of websites, usability measures the quality of the user experience when interacting with a web page. Accessibility is usability by people with disabilities.

User Agent - any software that can access websites, including web browsers, mobile applications, extensions and plug-ins, and assistive technologies that retrieve and present web content to users.

VoiceOver - an inbuilt screen reader for Apple Inc.'s products like iPhones, Macbooks, and so on.

W3C/WAI (World Wide Web Consortium / Web Accessibility Initiative) - develops standards and support materials that help you understand and implement accessibility the main international standards organization for the Internet.

WebAIM - (Web Accessibility In Mind) - a non-profit organization based at the Center for Persons with Disabilities at Utah State University that is one of the leading providers of web accessibility expertise internationally.

WCAG (Web Content Accessibility Guidelines) - set of web accessibility guidelines published by the W3C, which are the main internationally agreed upon standards for the World Wide Web, established to help content authors and developers create web content that is accessible for people of all abilities and disabilities.