Glossary

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Form Label(also: Input Label, Form Field Label)

A text label programmatically associated with an interactive form control (such as a text input, button, checkbox, or dropdown) that identifies the purpose or function of that control to all users. In HTML, form labels are typically implemented using the <label> element linked…

GAIA(also: Guidelines for Accessible Interfaces for people with Autism, Guidelines for Accessible Interfaces for Autism)

A set of design guidelines specifically developed to make digital interfaces more accessible for autistic users. GAIA addresses common barriers that autistic people face when using technology, including sensory overload from animations and complex layouts, difficulty with…

General Data Protection Regulation(also: GDPR)

A European Union regulation (2016/679) that governs the collection, processing, and storage of personal data for individuals within the EU and EEA. GDPR requires that consent for data processing be freely given, specific, informed, and unambiguous—which has significant…

HHS Usability Guidelines(also: Research-Based Web Design and Usability Guidelines, Usability.gov Guidelines)

A comprehensive set of evidence-based web design and usability guidelines published by the U.S. Department of Health and Human Services (HHS). The guidelines cover areas including homepage design, page layout, navigation, scrolling, headings, links, text appearance, content…

Heading Structure(also: Header Hierarchy, Heading Levels, Document Outline)

The hierarchical organization of headings (H1 through H6 in HTML) used to define the logical structure and sections of a document or web page. Proper heading structure is one of the most critical accessibility features for screen reader users, who rely on headings to skim…

Hypermedia

An extension of hypertext that incorporates multimedia content — audio, video, images, and animation — alongside text, all linked in a non-linear structure. What distinguishes hypermedia from hypertext is the implied sequencing required for time-based media: a video contains…

Hypertext

A way of organising and presenting textual content in a non-linear manner by breaking it into fragments and describing the relationships between them. A book has chapters in a fixed order, but hypertext allows content to be navigated in multiple paths through links between…

IAccessible2(also: IA2)

An open accessibility API specification originally developed by IBM and donated to the Linux Foundation. IAccessible2 extends Microsoft Active Accessibility (MSAA) to support the richer semantic information needed by Web 2.0 applications, including WAI-ARIA roles, states, and…

ICADD(also: International Committee on Accessible Document Design)

A non-profit organization that developed techniques for making structured electronic documents accessible to people with print disabilities. ICADD created the SDA (SGML Document Access) mechanism — a set of attributes that map complex document type definitions to a simplified…

ICF(also: International Classification of Functioning, Disability and Health)

A framework developed by the World Health Organization (WHO) and endorsed by all 191 member states in 2001 for describing and measuring health and disability. The ICF takes a biopsychosocial approach, classifying functioning and disability across four components: body functions…

ICT Accessibility(also: Information and Communication Technology Accessibility)

The design and development of information and communication technology products and services so they can be used by people with the widest range of abilities, including those with visual, hearing, motor, and cognitive disabilities. ICT accessibility encompasses hardware,…

IIIF(also: International Image Interoperability Framework, Triple-I-F)

The International Image Interoperability Framework (IIIF) is a set of open, community-developed technical specifications and APIs that enable cultural heritage institutions to share, access, and reuse digital image collections in a standardised way. IIIF provides an Image API…

IMS AccessForAll(also: AccLIP, IMS Accessibility for LIP, AccessForAll)

A specification from IMS Global Learning Consortium that defines how to describe learner accessibility preferences and match them with appropriate learning resources. IMS AccessForAll extends the IMS Learner Information Package (LIP) with detailed accessibility preference…

IMS Content Packaging(also: IMS CP, Content Package)

IMS Content Packaging is a specification from the IMS Global Learning Consortium that defines a standard way to bundle and exchange digital learning content between different learning management systems and educational platforms. A content package consists of a manifest file…

ISCII(also: Indian Script Code for Information Interchange)

A character encoding standard developed by the Government of India for representing Indian language text in digital systems. ISCII uses a single encoding scheme that can represent characters from all major Indian scripts by exploiting their common phonetic structure — each…

ISO 24751(also: ISO/IEC 24751, Individualized Adaptability and Accessibility in E-Learning)

ISO 24751 (Individualized Adaptability and Accessibility in E-Learning, Education and Training) is an international standard for matching the accessibility features of digital learning resources and environments to the needs and preferences of individual learners. Published in…

ISO 9241-210(also: Human-Centred Design Standard, Ergonomics of Human-System Interaction — Part 210)

An international standard specifying the principles and activities of human-centred design (HCD) for interactive systems. It defines a six-step iterative process — understanding context of use, specifying user requirements, producing design solutions, and evaluating against…

Keyboard Accessibility(also: Keyboard Navigation, Keyboard Operability)

The principle and practice of ensuring that all functionality of a website, application, or digital interface can be accessed and operated using only a keyboard, without requiring a mouse, touchscreen, or other pointing device. Keyboard accessibility is foundational to web…

Learning Design(also: IMS Learning Design, IMS LD)

A specification from IMS Global Learning Consortium (based on the Educational Modeling Language) that provides a framework for describing the structure and sequence of learning activities, roles, and environments in educational scenarios. Learning Design enables the separation…

Learning Object Metadata(also: LOM, IEEE LOM)

A data model used to describe learning resources, standardized by IEEE (IEEE 1484.12.1). Learning Object Metadata defines a set of elements organized into categories including general, lifecycle, technical, educational, and rights information. For accessibility, LOM is…

Legal blindness(also: Legally blind)

A level of visual impairment defined in many jurisdictions as visual acuity of 20/200 or worse in the better eye with best correction, or a visual field of 20 degrees or less. Legal blindness is an administrative threshold used to determine eligibility for disability benefits…

Logical Reading Order(also: Reading Sequence, Programmatic Reading Order)

The sequence in which content within a document is presented to assistive technologies, which should match the intended logical flow of the content as a human reader would understand it. In PDFs, the logical reading order is determined by the tag tree structure, not the visual…

Luminance(also: Relative Luminance)

The relative brightness of a color as perceived by the human eye, measured on a scale from 0 (black) to 1 (white). In accessibility, relative luminance is the foundation of WCAG color contrast ratio calculations, which compare the luminance of foreground text against its…

Luminous Efficiency Function(also: LEF, Spectral Luminous Efficiency Function, V(lambda))

A function that describes how the human visual system converts light intensity at different wavelengths into perceived brightness. The standard LEF used in WCAG contrast ratio calculations is based on a "standard observer" with typical colour vision. However, people with CVD —…

MIDI(also: Musical Instrument Digital Interface)

A technical standard for communication between electronic musical instruments, computers, and related audio devices. MIDI transmits digital messages representing musical events like note-on, note-off, velocity, and control changes rather than audio signals. Because MIDI data is…

MPEG-4 Facial Action Parameter(also: MPEG-4 FAP, FAP, Facial Action Parameter)

A standard for 3D face animation defined in ISO/IEC 14496-2 (MPEG-4), which parameterises a face through 68 feature points whose displacements (scaled relative to the character's own facial proportions) encode any facial expression. MPEG-4 FAP is proportion-invariant, so the…

MathML(also: Mathematical Markup Language)

A W3C standard XML-based markup language for describing mathematical notation and its structure, enabling mathematical content to be rendered visually in web browsers and read aloud by screen readers. MathML is essential for STEM accessibility because it encodes both the visual…

MathML(also: Mathematical Markup Language)

A W3C standard XML-based markup language for describing mathematical notation and capturing both its structure and content. MathML comes in two forms: presentation MathML, which describes how a formula looks (layout and visual appearance), and content MathML, which describes…

Matterhorn Protocol(also: PDF Association Matterhorn Protocol)

A comprehensive set of test conditions published by the PDF Association for verifying PDF/UA (ISO 14289-1) conformance. The Matterhorn Protocol categorizes accessibility checks into those that can be performed by automated tools and those that require human judgment, providing a…

Metadata

Data that provides structured information about other data or digital content. In accessibility, metadata plays a critical role in describing the accessibility features and characteristics of digital resources — for example, indicating whether a document has alternative text for…

Mobile Web Accessibility(also: Mobile Accessibility)

The practice of ensuring websites and web applications are usable by people with disabilities when accessed through mobile devices such as smartphones and tablets. Mobile web accessibility presents unique challenges including small screen sizes, touch-based interaction, device…

Mobile Web Best Practices(also: MWBP, MWBP 1.0)

A W3C recommendation published in 2006 that defines good usability and accessibility practices for delivering web content to mobile devices. Derived from the Web Content Accessibility Guidelines 1.0 (WCAG 1.0), Mobile Web Best Practices focuses on guidelines that have a direct…

MusicXML

An open, XML-based standard format for representing Western musical notation, enabling the exchange of sheet music between different music notation software applications. MusicXML encodes the structural and visual elements of a musical score in a machine-readable format, making…

NCAM(also: National Center for Accessible Media)

A research and development facility at WGBH (Boston public media) that develops accessible media technologies and guidelines. NCAM created widely-adopted guidelines for describing STEM images (charts, graphs, diagrams) for people with visual impairments, developed through expert…

NIMAS(also: National Instructional Materials Accessibility Standard)

A technical standard in the United States that defines a consistent file format for producing accessible versions of print instructional materials. NIMAS is based on the DAISY/NISO standard and specifies how publishers must provide source files so they can be converted into…

National Transition Strategy (NTS)(also: NTS, Web Accessibility National Transition Strategy)

The Australian Government's National Transition Strategy was a formal policy established in June 2010 requiring all federal, state, and territory government websites to conform to WCAG 2.0. It set staged milestones — Level A conformance by December 2012 and Level AA by December…

Nemeth Code(also: Nemeth Braille Code for Mathematics and Science)

A specialized braille code developed by Abraham Nemeth for representing mathematics, science notation, and technical symbols. Nemeth Code provides a comprehensive system for expressing equations, fractions, subscripts, superscripts, and other mathematical constructs in braille.…

OpenDocument Format(also: ODF, OASIS ODF)

An open, XML-based file format standard for office documents maintained by OASIS (Organization for the Advancement of Structured Information Standards). ODF includes specifications for text documents, spreadsheets, presentations, and graphics. It incorporates accessibility…

OpenType(also: OpenType Font)

A font format developed by Microsoft and Adobe that supports advanced typographic features including glyph substitution (GSUB) and glyph positioning (GPOS). OpenType fonts are critical for correctly rendering complex scripts such as Indian languages, Arabic, and Thai, where the…

OpenXR

An open, royalty-free standard developed by the Khronos Group that provides a unified API for accessing VR and AR platforms and devices. OpenXR lets XR applications run across different headsets (Meta Quest, Valve Index, HTC Vive, Windows Mixed Reality, etc.) without…

PDF Accessibility(also: Accessible PDF, PDF A11y)

The practice of creating PDF documents that can be effectively used by people with disabilities, including those who use screen readers, keyboard navigation, magnification, or other assistive technologies. Accessible PDFs require proper document structure (tag trees with…

PDF/UA(also: ISO 14289, Universal Accessibility for PDF)

The international standard (ISO 14289) for accessible PDF documents. PDF/UA defines requirements for PDF content, PDF readers, and assistive technology to ensure accessible interaction with PDF documents. It builds on the existing PDF tag structure and requires proper reading…

POUR

The four foundational principles of WCAG: Perceivable (information must be presentable to users in ways they can perceive), Operable (user interface components must be operable), Understandable (information and operation of the user interface must be understandable), and Robust…

POUR Principles(also: POUR, Four Principles of Accessibility)

The four foundational principles of the Web Content Accessibility Guidelines (WCAG): Perceivable, Operable, Understandable, and Robust. Perceivable means information must be presentable in ways users can perceive (e.g., alt text for images, captions for video). Operable means…

Personalization Semantics(also: WAI-Adapt)

A W3C specification that defines standardized semantics enabling content to be adapted to individual user needs and preferences. Personalization Semantics allows web authors to add metadata attributes to HTML elements that describe their purpose, importance, or function in a way…

Plain language(also: Plain English, Easy read, Simple language)

A communication approach that uses clear, concise, and well-organised writing designed to be understood the first time it is read. Plain language avoids jargon, complex sentence structures, and ambiguous wording. It is a key accessibility practice for making information…

SAE Automation Levels(also: SAE J3016, Levels of Driving Automation)

A six-level classification system (0-5) defined by SAE International that describes the degree of vehicle automation. Level 0 provides no automation; Levels 1-2 offer driver assistance features; Level 3 provides conditional automation where the vehicle can drive but a human must…

SAPI(also: Speech Application Programming Interface, Microsoft SAPI)

The Speech Application Programming Interface (SAPI) is a Microsoft Windows API that enables applications to use speech recognition and text-to-speech synthesis. SAPI provides a standardized interface between speech engines and applications, meaning that a synthetic voice built…

SCORM(also: Sharable Content Object Reference Model)

A set of technical standards for e-learning software products, originally developed by the Advanced Distributed Learning (ADL) initiative. SCORM defines how learning content is packaged, sequenced, and communicated with Learning Management Systems (LMS), enabling…

SGML(also: Standard Generalized Markup Language)

An international standard (ISO 8879:1986) metalanguage for defining markup languages that describe the structure and content of electronic documents. SGML introduced foundational concepts including descriptive markup (tagging what content is, not how it should look), document…