Glossary

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Omnidirectional wheelchair(also: Holonomic wheelchair)

An electric wheelchair capable of moving in any direction — forward, backward, sideways, and diagonally — as well as rotating in place, typically using Mecanum wheels or similar omnidirectional drive systems. Unlike conventional wheelchairs that can only move forward and…

On Input(also: WCAG 3.2.2)

WCAG 2.1 success criterion 3.2.2 (Level A) requires that changing the setting of any user interface component does not automatically cause a change of context (e.g., submitting a form, navigating to a new page, or moving focus to another component) unless the user has been…

On-Body Gesture(also: On-Body Interaction, Body-Based Gesture)

A gesture performed on or against one's own body rather than on a device surface or in the air. Examples include tapping the thigh, swiping along the forearm, or touching the ear to trigger a command on a connected device. On-body gestures are explored as an alternative input…

On-Body Interaction(also: Body-centric interaction, Skin input, On-body input)

An interaction paradigm that uses the surface of the user's own body as an input medium, typically through gestures like taps, swipes, or touches on the skin. On-body interaction leverages tactile and proprioceptive feedback from the user's own body, making it potentially…

On-Demand Simplification(also: On-demand text simplification, User-initiated simplification)

An interaction pattern for Automatic Text Simplification reading-assistance tools in which the user explicitly requests a simpler version of a word, phrase, or sentence — typically via hover, click, or tap — rather than having the system pre-apply simplifications to the page…

On-Device Processing(also: Local Processing, Edge Processing)

Computing performed directly on a user's device (phone, tablet, or wearable) rather than sending data to external servers. On-device processing is particularly valuable for privacy-sensitive accessibility features because it keeps personal visual data under the user's control,…

On-Screen Keyboard(also: Virtual Keyboard, Software Keyboard, OSK)

A software application that displays a visual representation of a keyboard on the computer screen, allowing users to type by selecting keys with a pointing device, head tracker, eye gaze system, or switch. On-screen keyboards are essential assistive technology for people who…

On-Screen Text(also: OST, Visual Text, Burned-In Text)

Text that appears visually within video content, including titles, subtitles, captions, signs, labels, credits, and any other written information displayed on screen. On-screen text must be read aloud or referenced in audio descriptions to ensure BLV users have access to this…

On-body Input(also: Skin-based Input, Body-based Interaction)

An interaction technique that uses the surface of the user's own body — typically the hand, arm, or other skin areas — as an input surface for controlling digital devices. On-body input is sensed through wearable cameras, depth sensors, capacitive touch sensors, or acoustic…

On-device Recognition(also: On-Device Inference, Edge Recognition)

Performing pattern recognition - such as sign language recognition, speech recognition, or computer vision - locally on the user's device rather than by sending input to a remote server. On-device recognition matters for accessibility because it preserves privacy (camera or…

One-Handed Input(also: Single-Handed Operation, One-Handed Operation)

One-handed input refers to interaction techniques and interface designs that can be operated using a single hand, accommodating users who have limited use of one limb due to amputation, hemiplegia, stroke, cerebral palsy, or other physical conditions. One-handed input methods…

Online Accessibility Act(also: OAA, US Online Accessibility Act)

A proposed US federal law (H.R. 1100, introduced in the 117th Congress) that would require consumer-facing websites and mobile apps of covered organisations to comply with Web Content Accessibility Guidelines (WCAG). The OAA is intended to close an ambiguity in the existing…

Online Braille(also: Web Braille, Digital Braille, Electronic Braille)

Online Braille refers to Braille content that is generated, distributed, or accessed through the Internet or digital platforms, as opposed to traditional embossed paper Braille. This includes web-based Braille translation services, downloadable Braille-formatted files such as…

Online Community(also: Virtual Community, Online Forum)

A group of people who interact and share information through internet-based platforms such as mailing lists, forums, social media groups, or Q&A sites. For people with disabilities, online communities serve as critical resources for sharing accessibility knowledge,…

Online Disability Community(also: Disability Online Forum, Digital Disability Community)

Internet-based spaces where people with disabilities connect to share experiences, seek advice, provide peer support, and collaborate on problem-solving. Platforms like Reddit, Facebook groups, and specialized forums serve as vital resources for knowledge exchange about…

Online Focus Group(also: Virtual Focus Group, Remote Focus Group)

A qualitative research method in which a group of participants discusses a topic through an online platform rather than meeting in person. Online focus groups are particularly valuable for accessibility research because they remove physical barriers — such as transportation,…

Online Health Communities(also: OHCs)

Internet-based communities where people affected by a shared health condition exchange experiential knowledge, emotional support, and practical coping strategies. Traditionally hosted on dedicated forums, OHCs increasingly exist as “unbounded” communities on mainstream social…

Online Health Community(also: OHC, Digital Health Community, Online Support Group)

A digital space where individuals with shared health conditions, disabilities, or wellness concerns connect to exchange information, provide emotional support, share experiences, and discuss treatment options. Traditional OHCs are typically hosted on dedicated forums or…

Online Peer Support(also: Digital Peer Support, Online Mutual Aid)

The exchange of information, emotional encouragement, and practical advice between individuals with shared experiences through digital platforms such as forums, social media groups, and dedicated support communities. For people with disabilities, online peer support provides…

Onomatopoeia

Words that phonetically imitate or suggest the sound they describe, such as "buzz," "crash," "swoosh," or "sizzle." In captioning, onomatopoeia is one approach to representing non-speech sounds, offering viewers a sense of the acoustic quality of a sound. However, research shows…

Ontology(also: Web Ontology, Knowledge Ontology)

In computing and information science, a formal representation of knowledge within a domain, consisting of concepts, categories, properties, and the relationships between them. Ontologies enable machines to reason about and process domain knowledge in structured ways. In…

Open Captioning(also: Open Captions, Burned-In Captions)

Captions that are permanently embedded into the video image and cannot be turned off by the viewer. Unlike closed captions, open captions are part of the visual content itself, making them visible to all viewers regardless of device or platform support. Open captions are…

Open Captions(also: Burned-in Captions, Hard-coded Captions)

Captions that are permanently embedded into a video and cannot be turned off by the viewer. Unlike closed captions, which can be toggled on or off, open captions are always visible as part of the video image itself. Open captions are sometimes used when a platform does not…

Open Data(also: Open Government Data, Public Data)

Data that is published and made freely available to everyone without copyright or patent restrictions, following the premise that transparency enables public accountability and innovation. In accessibility, open data initiatives publish information about the accessibility of…

Open Data(also: Open Government Data)

Data that is freely available to anyone to use, redistribute, and republish without restrictions from copyright, patents, or other control mechanisms. In the accessibility context, open data initiatives by governments and transport authorities — such as publishing station…

Open Educational Resources(also: OER)

Teaching, learning, and research materials in any medium that are freely available for use, adaptation, and redistribution. OER can include textbooks, course materials, videos, assessments, and software tools, typically released under open licenses such as Creative Commons.…

Open Sound Control(also: OSC)

An open, network-based protocol for communication between computers, sound synthesizers, and other multimedia devices, developed by Matthew Wright and Adrian Freed (1997). OSC sends human-readable address patterns and floating-point values over UDP/TCP, offering higher…

Open Source(also: Open-Source Software, OSS, FOSS)

Software whose source code is publicly available and can be freely used, modified, and distributed, typically developed collaboratively through platforms like GitHub. Open-source development models have significant implications for accessibility: they enable disabled users to…

Open access(also: OA, Open access publishing)

A publishing model that makes scholarly research freely available to anyone online, removing subscription paywalls that traditionally restrict access to academic journals. While open access has significantly democratised access to knowledge, research has shown that the shift…

Open-Source Hardware(also: OSHW)

Physical devices and components whose design specifications are publicly available for anyone to study, modify, distribute, and manufacture. In the assistive technology space, open-source hardware enables global sharing of device designs that communities can adapt to local needs…

Open-Vocabulary Detection(also: Open-Vocabulary Object Detection, OVD)

A class of computer vision object detection models that accept arbitrary text queries at inference time rather than being restricted to a fixed set of pre-trained classes. Instead of only recognizing, for example, the 80 COCO categories, an open-vocabulary detector (such as…

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…

OpenDyslexic(also: Open Dyslexic)

A free, open-source typeface specifically designed to improve readability for people with dyslexia. The font uses heavier bottom portions on letters to help prevent visual rotation and uses unique letter shapes to reduce confusion between similar characters. However,…

OpenMath

An XML-based standard for representing mathematical objects and their semantics in a machine-readable format. Unlike MathML, which has both presentation (visual layout) and content (semantic structure) modes, OpenMath focuses purely on semantic meaning, defining mathematical…

OpenPose

An open-source computer vision library developed by Carnegie Mellon University that detects human body, hand, facial, and foot keypoints in real-time from images or video. OpenPose extracts 25 body keypoints, 21 keypoints per hand, and 70 facial landmarks, providing a skeletal…

OpenSCAD

An open-source, code-based 3-D computer-aided design (CAD) application that uses a scripting language to define 3-D models through constructive solid geometry operations. Unlike visual modeling tools, OpenSCAD creates models from textual descriptions of geometric primitives and…

OpenStreetMap(also: OSM)

A free, collaborative, open-source mapping project that provides geographic data including roads, buildings, and points of interest, contributed and maintained by volunteers worldwide. OpenStreetMap is significant for accessibility because its open data can be freely used to…

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…

Operant Conditioning(also: Instrumental Conditioning, Operant Learning)

A learning process in which behaviour is modified by its consequences — specifically, by reinforcement (rewards that increase the likelihood of the behaviour) or punishment (consequences that decrease it). In accessibility research and clinical assessment, operant conditioning…

Opportunistic Accessibility(also: Opportunistic Accessibility Improvement)

Opportunistic accessibility is an approach to improving digital accessibility in which enhancements are automatically applied to the maximum extent possible without causing negative side effects. Rather than treating accessibility as an all-or-nothing goal, opportunistic…

Optacon(also: Optical-to-Tactile Converter)

A historical assistive device developed in the 1970s that enabled blind people to read printed text by converting visual images of letters into tactile vibration patterns felt with the fingertip. Users would move a small camera across printed text while their other hand rested…

Optic Ataxia(also: Visuomotor Ataxia)

A neurological condition characterised by impaired reaching for objects using visual guidance, despite having adequate vision and motor strength. People with optic ataxia can see an object and describe its location but struggle to accurately direct their hand toward it. This…

Optic Flow(also: Visual Flow, Optical Flow)

The pattern of apparent motion of objects, surfaces, and edges in a visual scene caused by relative movement between the observer and the scene. Optic flow provides critical information about self-motion, speed, direction, and the structure of the environment. It plays a key…

Optic Nerve Hypoplasia(also: ONH)

A congenital condition in which the optic nerve is underdeveloped, resulting in varying degrees of vision loss from mild visual impairment to complete blindness. It is one of the most common causes of visual impairment in children. People with optic nerve hypoplasia may…

Optic Neuropathy(also: Optic Nerve Disease)

Damage to the optic nerve that can result in vision loss, including reduced visual acuity, impaired color vision, and visual field defects. Optic neuropathy can be caused by various conditions including glaucoma, inflammation, ischemia, trauma, or toxic exposure. The pattern and…

Optic atrophy(also: Optic nerve atrophy)

A condition involving damage to the optic nerve that results in partial or complete loss of vision. The optic nerve carries visual information from the eye to the brain, and when its fibers degenerate, visual acuity, color perception, and peripheral vision can all be affected.…

Optical Braille Recognition(also: OBR)

A technology that uses cameras or optical sensors to detect and interpret embossed Braille characters, converting them into digital text. Optical Braille recognition works by capturing images of Braille pages and analysing the patterns of raised dots — typically by detecting…

Optical Character Recognition(also: OCR, Text Recognition)

Technology that converts images of text—whether typed, handwritten, or printed—into machine-readable text data. OCR is used in accessibility to extract text from images, documents, video frames, and real-world scenes, enabling screen readers to read text that would otherwise be…

Optical Character Recognition (OCR)(also: OCR, Text Recognition)

Technology that converts images of text — such as scanned documents, photographs of signs, or PDF pages stored as images — into machine-readable text that can be processed by screen readers, search engines, and other software. OCR is a critical tool for making scanned documents…