Glossary

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R(also: R Programming Language, R Project, R Statistical Computing)

A free, open-source programming language and software environment widely used for statistical computing, data analysis, and graphical representation. R is the standard tool for statisticians in both academia and industry, offering extensive libraries for creating data…

RACI Matrix(also: RACI chart, Responsibility Assignment Matrix)

A project-management tool that maps tasks to stakeholders using four roles: Responsible (does the work), Accountable (owns the outcome), Consulted (provides input), and Informed (kept in the loop). Accessibility teams use RACI matrices to clarify who within a cross-functional…

RAG(also: Retrieval-Augmented Generation)

An AI architecture pattern that pairs a large language model with an external knowledge store (typically a vector index of text chunks) so that, for each user query, relevant documents are retrieved first and injected into the prompt before the model generates a response. RAG…

RANSAC(also: Random Sample Consensus)

An iterative algorithm (Fischler and Bolles, 1981) for fitting a mathematical model to data that contains a significant proportion of outliers. In accessibility-focused indoor navigation systems, RANSAC is commonly used to detect the floor plane from a LiDAR point cloud — points…

RAVEN(also: Rule-based Accessibility Validation Environment)

An accessibility testing tool developed by IBM as a set of Eclipse IDE plug-ins for verifying the accessibility of graphical user interface applications. RAVEN uses aspect-oriented programming techniques to provide non-invasive, automatic to semi-automatic accessibility…

RDF(also: Resource Description Framework)

A W3C standard for describing resources on the web using a graph-based data model of subject-predicate-object triples. RDF provides a foundation for the Semantic Web by enabling machine-readable metadata that can describe relationships between web resources, including…

REAPER(also: Rapid Environment for Audio Production, Engineering, and Recording)

A digital audio workstation (DAW) software application developed by Cockos that is known for its relatively strong accessibility support compared to other professional DAWs. When used with the OSARA (Open Source Accessibility for the REAPER Application) extension, REAPER…

RESOLV Icons(also: Representational Enumerated Semi-transparent Overlaid Labels for Voice)

A visual disambiguation technique for voice interfaces where semi-transparent numbered labels are overlaid on screen elements that match an ambiguous voice command. When a user speaks a command that could refer to multiple targets, RESOLV icons appear next to each matching…

RFID(also: Radio Frequency Identification, RFID Tag)

A technology that uses electromagnetic fields to automatically identify and track tags attached to objects. RFID tags contain electronically stored information that can be read by RFID readers without line-of-sight contact. In accessibility applications, RFID enables physical…

RGB-Depth Camera(also: RGB-D camera, Depth camera)

A camera that captures both a conventional colour image (RGB) and a per-pixel depth map, usually via structured light, time-of-flight, or stereo sensing. RGB-D cameras are widely used in assistive navigation systems for people who are blind because they enable real-time…

RGBD Camera(also: RGB-D Camera, Depth Camera, Stereo Camera)

A camera that captures both a colour (RGB) image and a per-pixel depth (D) measurement of the scene, yielding a 3D representation of the environment. Depth can be produced by stereo vision, structured light, or time-of-flight sensing. In accessibility research RGBD cameras…

RNIB(also: Royal National Institute of Blind People, Royal National Institute for the Blind)

The largest charity supporting blind and partially sighted people in the United Kingdom, providing services including accessible format transcription, assistive technology advice, employment support, and advocacy. The RNIB operates one of the world's leading music transcription…

RSSI(also: Received Signal Strength Indicator, Received Signal Strength Index)

A measurement of the power level of a radio signal received by a device, commonly used in Bluetooth and Wi-Fi based indoor positioning systems. In accessible indoor navigation, RSSI readings from BLE beacons are used to estimate a user's distance from each beacon — stronger…

RSSI Fingerprinting(also: Received Signal Strength Fingerprinting, Radio Fingerprinting, Signal Fingerprinting)

An indoor localization technique in which a device estimates its position by comparing the current pattern of received signal strengths (RSSI) from surrounding radio sources — most commonly Bluetooth Low Energy beacons or Wi-Fi access points — against a pre-collected map of…

Radial Direction(also: Angular Direction, Heading, Bearing (audio display))

In auditory-display research, a data value that represents a direction in a plane — for example a compass bearing, the tangent of a curve, or the orientation of a pointer — treated as an angle rather than as a pair of Cartesian coordinates. Radial values are inherently circular…

Raised Line Drawing(also: Raised Line Graphic, Tactile Line Drawing, Swell Paper Drawing)

A graphic representation in which lines and shapes are physically raised above the surface of paper or another substrate so they can be perceived by touch. Raised line drawings are a fundamental tool for making visual information accessible to blind and low-vision users,…

Raised-Line Drawing(also: Raised-Line Picture, Tactile Line Drawing, Embossed Line Drawing)

A raised-line drawing is a tactile representation of a visual image created by producing elevated lines on a surface that can be felt by touch, enabling blind and visually impaired people to perceive graphical information through their fingertips. Raised-line drawings can be…

Random Forest Classifier(also: Random Forest)

A machine learning algorithm that creates multiple decision trees during training and outputs the class that is the mode of the individual trees predictions. Random forests are widely used in gesture recognition, activity recognition, and other classification tasks in assistive…

Random Walk(also: Random Walk Sampling)

In web-accessibility evaluation, a random walk is a probabilistic sampling method that starts from a seed page (typically the home page) and follows outgoing links according to a probability rule — for example, with probability d follow a uniformly-chosen outgoing link, and with…

Randomization Test(also: Randomisation Test, Permutation Test)

A randomization test (also called a permutation test) is a non-parametric statistical test that computes a p-value by re-shuffling the observed data many times under the null hypothesis and asking how often the re-shuffled data produce a test statistic as extreme as the one…

Range of Motion(also: ROM)

The full extent of movement possible at a joint, measured in degrees of rotation or linear distance. Range of motion is a fundamental clinical measurement used by occupational and physical therapists to assess hand, wrist, elbow, and shoulder function. In accessibility contexts,…

Range of Motion(also: ROM, Joint Mobility)

The full movement potential of a joint, measured in degrees of a circle, from the starting position to maximum extension or flexion. Range of motion exercises are fundamental to physical rehabilitation, helping maintain joint flexibility and prevent contractures. In…

Rapid Auditory Processing(also: RAP, Auditory Temporal Processing)

The ability to perceive and process rapidly changing auditory signals that occur within tens of milliseconds, such as the rapid frequency and amplitude transitions that characterise speech sounds. Rapid auditory processing is a fundamental skill for language acquisition, as…

Rapid Prototyping

The fast fabrication of a physical model or functional prototype using computer-aided design and manufacturing technologies like 3D printing. In assistive technology development, rapid prototyping enables quick iteration on device designs, allowing makers to test and refine…

Rapid Serial Visual Presentation(also: RSVP)

A text display method in which words or short phrases are shown one at a time in a fixed location on screen in quick succession, eliminating the need for eye movements (saccades) between words. RSVP was first proposed in the 1950s for reading research and adapted for practical…

Ray Casting(also: Raycasting)

An interaction technique in 3-D environments where an invisible ray is projected from a point (such as a user's finger position or controller) into the virtual scene to determine which object the ray intersects first. In VR accessibility, ray casting translates 2-D touch input…

Re-identification risk(also: De-anonymization risk, Data re-identification)

The possibility that an individual can be identified from supposedly anonymized data by combining multiple data points or matching against external datasets. People with disabilities face heightened re-identification risk because uncommon combinations of attributes — rare…

Re-narration(also: Web Re-narration, Content Re-narration)

The process of creating alternative versions of web content — such as translations, simplifications, audio descriptions, or culturally adapted media — to make it accessible to audiences who cannot effectively use the original. Unlike simple translation or metadata repair,…

Re-speaking(also: Respeaking, Speech-to-Text Relay)

A captioning technique in which a trained operator listens to a speaker and repeats (re-speaks) their words clearly into a high-quality microphone in a controlled environment, allowing automatic speech recognition software to generate captions with higher accuracy than direct…

Reach Envelope(also: Workspace Envelope, Reach Zone, Comfort Zone)

The three-dimensional volume of space that a person can physically access with their hands or arms from a given position, taking into account their specific motor abilities, range of motion, and comfort levels. For people with upper extremity mobility impairments — such as those…

Reacher(also: Grabber, Reacher-Grabber, Grabber Tool)

A reacher (also called a grabber or reacher-grabber) is a low-cost handheld assistive device — typically a lightweight aluminum or plastic shaft 60-90 cm long with a trigger handle at one end and a pair of gripping jaws at the other — used by people with limited reach, mobility,…

Reaching Time(also: Navigation Time, Time to Target)

A usability metric measuring the time required for a user to navigate to a specific element on a web page. For blind users employing screen readers, reaching time is a key indicator of page navigability and efficiency, as it captures the cumulative cost of navigating through and…

Read-Along(also: Read Along, Synchronised Highlighting, Karaoke-style Highlighting)

An accessibility pattern in which on-screen text is highlighted word-by-word or phrase-by-phrase in synchronisation with spoken audio. Used in children's reading apps, language-learning tools, accessible ebook formats (e.g., EPUB Media Overlays), and podcast players.…

Read-Aloud Technology(also: Read-Aloud Feature, Text Read-Aloud)

Technology that converts written text to spoken audio output, allowing users to listen to content rather than or in addition to reading it visually. Read-aloud technology differs from general text-to-speech in its focus on synchronized presentation — highlighting words or…

Readability(also: Text Readability)

The ease with which a reader can read and understand written text. Readability encompasses both visual readability (typography, layout, color contrast, spacing) and linguistic readability (vocabulary complexity, sentence structure, text organization). In accessibility contexts,…

Readability(also: Text Readability)

The ease with which written text can be read and understood, determined by factors including vocabulary complexity, sentence length, grammatical structure, and text organisation. Readability is distinct from legibility (which concerns the visual clarity of individual characters…

Readability formula(also: readability metric, readability index, readability measure)

A mathematical formula that estimates the difficulty of reading a text, typically based on features like sentence length, word length, syllable count, or vocabulary frequency. Common formulas include Flesch Reading Ease, Flesch-Kincaid Grade Level, SMOG, and Gunning Fog Index.…

Readily Achievable(also: Readily Achievable Barrier Removal)

A legal concept from the Americans with Disabilities Act (ADA) meaning that barrier removal is easily accomplishable and able to be carried out without much difficulty or expense. What qualifies as readily achievable is measured in context — large, well-resourced organizations…

Reading Assistance(also: Reading Assistance Technology, Reading Support Tools)

Reading assistance refers to technologies and strategies that help people understand written text more easily. This includes tools like text-to-speech, automatic text simplification, screen readers, reading rulers, and dictionary lookups. For accessibility, reading assistance is…

Reading Assistant(also: Reading Aid, Reading Machine)

An assistive technology device or software application that helps people with visual impairments or reading disabilities access printed or displayed text. Reading assistants may use optical character recognition to convert text images to speech, magnification to enlarge text, or…

Reading Comprehension(also: Text Comprehension)

The ability to understand, interpret, and derive meaning from written text. Reading comprehension involves multiple cognitive processes including decoding words, activating background knowledge, making inferences, and monitoring understanding. It is a key target for reading…

Reading Disability(also: Reading Difficulty, Reading Disorder)

A condition that impacts a person's ability to read and develop literacy skills. Reading disabilities encompass a wide range of conditions including dyslexia, alexia, and difficulties arising from intellectual disabilities, cognitive impairments, sensory disabilities, or…

Reading Fluency

The ability to read connected text accurately, at an appropriate pace, and with proper expression - distinct from word-level decoding skill on one side and from reading comprehension on the other. Fluency is typically measured along three dimensions: accuracy (proportion of…

Reading Level(also: Grade Level, Reading Grade Level)

An estimate of the education or skill level a reader needs to understand a text, usually expressed as a U.S. school grade (e.g., grade 4) or an equivalent band. Reading level is the target output of most readability formulas and automatic readability assessment systems, and it…

Reading Literacy(also: Print Literacy, Text Literacy)

The ability to read and comprehend written text. In accessibility research with Deaf and Hard of Hearing populations, reading literacy is an important consideration because English literacy rates are statistically lower among deaf adults in the United States compared to the…

Reading Model(also: Theory of Reading)

A theoretical framework that explains the cognitive processes involved in reading and how reading skills develop. Key reading models include the Simple View of Reading (comprehension = decoding × language comprehension) and the Rope Model (which describes fluent reading as the…

Reading Order(also: Logical Reading Order, Narration Order)

The sequence in which content is presented to assistive technology users, particularly screen reader users, when navigating a document or web page. For sighted users, the visual layout of a document (columns, sections, sidebars) implicitly suggests a reading flow, but screen…

Reading Speed(also: Reading Rate, Words Per Minute)

The pace at which a person can read and process text, typically measured in words per minute. Reading speed is a common metric in evaluating reading support technologies and varies significantly among people with different disabilities. People with dyslexia often experience…

Reading Support Technology(also: Reading Assistive Technology, Reading Aid)

Any technology designed to make reading more accessible for people with disabilities, encompassing tools that support decoding, comprehension, readability, navigation, and literacy development. Reading support technologies range from visual augmentations and text simplification…

Reading accessibility(also: Readable content, Text accessibility)

The design of written content and reading interfaces to be usable by people with diverse literacy levels, cognitive abilities, language backgrounds, and sensory capabilities. Reading accessibility encompasses plain language, text simplification, adjustable typography (font size,…