Glossary

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Upper Baseline(also: Gold Standard, Reference Standard)

In accessibility evaluation research, an upper baseline is a high-quality reference stimulus used to establish the best achievable performance against which other systems are compared. For sign language animation studies, this might be a video of a human signer or a carefully…

Upper Body Motor Impairment(also: Upper Limb Impairment, Upper Extremity Disability)

A condition affecting the motor function of the arms, hands, or upper body that limits or prevents the use of standard input devices such as keyboards, mice, and touchscreens. Upper body motor impairments can result from conditions including amputation, cerebral palsy, spinal…

Upper Limb Impairment(also: Upper Extremity Impairment, Upper Body Impairment)

Reduced function in one or both arms, hands, or fingers due to conditions such as amputation, paralysis, muscular disorders, spasticity, or joint conditions. In VR and technology accessibility, upper limb impairment is particularly significant because most interaction paradigms…

Upper Limb Motor Impairment(also: Upper Extremity Motor Disability, Hand and Arm Motor Impairment)

A condition affecting movement, strength, coordination, or fine motor control in the hands, wrists, arms, or shoulders that impacts a person's ability to use standard computer input devices. Causes include cerebral palsy, spinal cord injury, stroke, multiple sclerosis,…

Upper Ontology(also: Foundation Ontology, Top-level Ontology)

An upper ontology is a high-level, domain-independent ontology that describes very general concepts — such as 'object', 'role', 'event', 'time', or, in a web-accessibility context, generic structural roles like 'menu', 'navigation', 'content region', or 'decoration'. It is…

Upper-Body Motor Impairment(also: Upper Extremity Impairment, Upper Limb Impairment)

Motor impairments affecting the upper extremities — including the arms, hands, fingers, shoulders, and neck — that limit a person's ability to perform tasks requiring fine motor control, gross motor movements, or upper-body strength. Common causes include spinal cord injury,…

Upper-Limb Amputation(also: Upper Limb Amputation, Arm Amputation)

The surgical or traumatic removal of all or part of an arm — including transhumeral (above elbow), transradial (below elbow), wrist disarticulation, and partial-hand levels. People with upper-limb amputation may use body-powered or myoelectric prostheses, or may choose no…

Upper-Limb Impairment(also: Upper Extremity Impairment, Arm Impairment, Hand Impairment)

A physical disability affecting the arms, hands, or fingers that limits a person's ability to perform fine motor tasks such as typing, using a mouse, or operating touchscreen devices. Upper-limb impairments can result from conditions including spinal cord injury, stroke,…

Upper-Limb Prosthetic(also: Upper Limb Prosthesis, Arm Prosthetic, Hand Prosthetic)

A prosthetic device that replaces or augments part or all of a missing upper limb — fingers, hand, wrist, forearm, or full arm. Upper-limb prosthetics range from passive cosmetic devices and body-powered cable-driven hands to externally powered myoelectric systems that read…

Urban Accessibility(also: City Accessibility, Built Environment Accessibility)

The degree to which urban environments, including streets, buildings, public spaces, and transportation systems, can be navigated and used by people with disabilities. Urban accessibility encompasses physical infrastructure such as curb cuts, tactile paving, and accessible…

Usability(also: Ease of Use)

Usability is the extent to which a product, system, or service can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use, as defined by ISO 9241-11. It goes beyond mere accessibility compliance to…

Usability Barrier

A type of access barrier where a task can technically be completed but not with the desired qualities such as speed, ease, accuracy, or comfort. Unlike failure point barriers, the task is possible, but the experience of completing it is unsatisfactory. For example, a web page…

Usability Engineering

A systematic, structured approach to designing and evaluating user interfaces that applies engineering principles to usability. Usability engineering involves defining measurable usability goals, conducting user analysis, iterative prototyping, and empirical testing with…

Usability Heuristics(also: Nielsen's Heuristics, Nielsen Heuristics, 10 Usability Heuristics)

A set of ten general principles for user interface design developed by Jakob Nielsen (originally with Rolf Molich in 1990, refined in 1994): visibility of system status, match between system and the real world, user control and freedom, consistency and standards, error…

Usability Study(also: Usability Test, Usability Evaluation)

A research method that evaluates how easily and effectively users can interact with a product, system, or prototype by observing real users performing tasks. Usability studies measure factors such as task completion rate, error frequency, time on task, and subjective…

Usability Testing(also: Usability Evaluation, User Testing)

A research method in which representative users attempt realistic tasks with a product or prototype while researchers observe and collect data on effectiveness, efficiency, and satisfaction. In accessibility contexts, usability testing with people with disabilities is essential…

Usable Accessibility

Usable accessibility is the principle that meeting technical accessibility standards (such as WCAG compliance) is necessary but not sufficient for ensuring that people with disabilities can effectively use digital products. A website may be technically accessible — screen…

Usage analytics(also: Telemetry, Interaction logging)

The collection and analysis of data about how users interact with a technology system in real-world settings, including session duration, feature usage frequency, settings preferences, and interaction patterns over time. In assistive technology research, large-scale usage…

Useful Field of View(also: UFOV, Functional Visual Field)

The useful field of view (UFOV) is the area of the visual field from which a person can extract information in a single glance without moving their eyes or head. Unlike the anatomical visual field, the UFOV is a measure of functional vision that depends on cognitive processing…

User Agency(also: User Control, User Autonomy)

The degree to which users maintain control over their interactions with a system, including the ability to make choices, adjust system behavior, override automated decisions, and understand what the system is doing on their behalf. In accessibility and AI-powered tools, user…

User Agent(also: Browser, Web Browser)

In web accessibility, a user agent is any software that retrieves, renders, and facilitates user interaction with web content. This includes mainstream web browsers like Chrome, Firefox, and Safari, as well as assistive technologies such as screen readers that work alongside…

User Agent Accessibility Guidelines(also: UAAG)

W3C guidelines that explain how to make user agents—web browsers, media players, and other applications that render web content—accessible to people with disabilities. UAAG covers how user agents should support accessibility features built into web content, provide their own…

User Elicitation(also: Elicitation study, Gesture elicitation study, User-defined gestures)

A participatory user-research method, widely used in gesture and interaction design, in which end users or domain experts are shown a desired system effect (a "referent" such as "rotate this object") and asked to propose the input action they believe should trigger it.…

User Empowerment(also: Design for User Empowerment)

A design philosophy that prioritizes giving users, particularly people with disabilities, the agency and tools to solve their own problems, customize their experiences, and participate as active creators rather than passive consumers of technology. Coined in accessibility…

User Enactment(also: UE, Experience Prototyping)

A research method in which participants explore emerging or future technologies through simulated scenarios using physical enactment stages (mockup environments). User enactment combines brainstorming, where participants speak aloud their thoughts and decisions, with…

User Engagement Scale(also: UES, UES-SF)

A validated self-report questionnaire for measuring user engagement with digital systems across dimensions including focused attention, perceived usability, aesthetic appeal, and reward. Developed by O'Brien and Toms and later shortened to the 12-item UES Short Form (UES-SF),…

User Experience(also: UX)

A person's perceptions and responses resulting from the use or anticipated use of a product, system, or service, encompassing emotions, beliefs, preferences, physical and psychological responses, and behaviours. Defined by ISO 9241-210, user experience goes beyond usability…

User Experience Questionnaire(also: UEQ, UEQ-S, Short UEQ)

A standardised self-report instrument, developed by Schrepp and colleagues, that captures a user's subjective impression of a product across dimensions such as attractiveness, efficiency, perspicuity, dependability, stimulation, and novelty via pairs of contrasting adjectives…

User Frustration(also: Computer Frustration, Technology Frustration)

The emotional response experienced by users when technology fails to meet their expectations or prevents them from completing tasks. User frustration can be caused by errors, confusing interfaces, inaccessible content, slow response times, or situations where the computer is…

User Interface Agent(also: Interface Agent, Software Agent, Assistant Agent)

A software component that observes user behaviour and the state of an application, then unobtrusively offers help — suggestions, shortcuts, summaries, or warnings — to reduce workload or prevent errors. In accessibility research, interface agents have been used to monitor a…

User Interface Management System(also: UIMS)

A software framework that separates user interface presentation and interaction from application logic, allowing the interface to be designed, modified, or replaced independently of the underlying program. A UIMS typically manages input handling, output rendering, and the…

User Modelling(also: User Modeling, User Profiling)

The process of creating and maintaining a digital representation of a user's characteristics, preferences, needs, and behaviours to personalise their interaction with a system. In accessibility contexts, user modelling captures information about a person's disabilities,…

User Participation(also: User Involvement, Participatory Research, Co-production)

The active involvement of end users in the design, development, and evaluation of products, services, or systems that affect them. In accessibility contexts, user participation means including people with disabilities not just as test subjects but as collaborators who contribute…

User Preference Profile(also: Customization Profile, Personalization Profile)

A stored set of user preferences and settings that can be automatically applied to new content, reducing the need for repeated manual customization. In video accessibility for ADHD, user preference profiles could store preferred layout, background, caption, and audio settings…

User Research(also: UX Research, Usability Research)

The systematic study of users and their needs, behaviours, and experiences to inform the design and development of products and services. User research methods include interviews, surveys, focus groups, usability testing, diary studies, contextual inquiry, and beta testing. In…

User Sensitive Inclusive Design(also: USID)

A design methodology proposed as an alternative to User Centred Design for populations with highly diverse and dynamically changing needs, particularly older people. User Sensitive Inclusive Design replaces "centred" with "sensitive" to acknowledge that it may be impossible to…

User Study(also: Usability Study, User Evaluation)

A research method in which participants interact with a system, tool, or interface while researchers observe, measure, and collect feedback on the user experience. User studies in accessibility research are essential for evaluating whether technologies actually meet the needs of…

User Testing(also: User Evaluation, End-User Testing)

A research method in which representative users perform tasks with a product or system while evaluators observe, record, and analyze their behavior. In accessibility contexts, user testing with people with disabilities is considered essential because it reveals real-world…

User model(also: User modeling, User modelling)

A computational representation of a user's characteristics, abilities, preferences, and behavior patterns, used to predict how they will interact with a system or to adapt an interface to their needs. In accessibility contexts, user models capture attributes such as motor range…

User persona(also: Persona, Design persona)

A fictional but research-based representation of a user archetype that captures key characteristics, goals, behaviours, and pain points of a segment of the target audience. In accessibility design, personas representing disabled users help development teams move beyond…

User profile(also: User model, Personal needs and preferences profile, PNP)

A structured collection of data describing a user's characteristics, capabilities, preferences, and requirements for interacting with a computing system. In accessibility, user profiles inform how interfaces should adapt to meet individual needs. Traditional approaches (such as…

User-Centered Design(also: UCD, Human-Centered Design)

A design philosophy and process that places the needs, preferences, and limitations of end users at the center of each stage of the design process. In accessibility contexts, user-centered design means actively involving people with disabilities not just as test subjects…

User-Centred Design(also: UCD, User-Centered Design, Human-Centred Design)

An iterative design methodology that places the needs, characteristics, and limitations of end users at the centre of each stage of the design process. In accessibility, user-centred design involves people with disabilities as active participants throughout design and…

User-Generated Captions(also: UGC captions)

Captions created and added to video content by non-professional contributors — typically the video's own creator or community members — rather than by professional captioners or fully automated systems. On social media, user-generated captions are often implemented as open…

User-Generated Content(also: UGC)

Content such as text, images, videos, and reviews created and shared by end users rather than by the website or platform owner. In e-commerce, user-generated content includes customer reviews, review photos, and Q&A sections. This content poses significant accessibility…

User-Generated Content(also: UGC, Prosumer Content)

Web content created and published by non-technical users through platforms like blogs, social media, wikis, and content management systems, rather than by professional web developers. The rise of user-generated content in Web 2.0 has created a significant accessibility…

User-Generated Content Accessibility(also: UGC Accessibility)

The practice of ensuring that user-generated content such as online reviews, forum posts, comments, and social media contributions is accessible to people with disabilities. Unlike curated website content, user-generated content poses unique accessibility challenges because it…

User-Sensitive Inclusive Design(also: USID)

A design methodology that adapts user-centered design principles for contexts where the target user population is highly diverse and where individual differences — including those related to disability — are significant design factors. Unlike Universal Design which aims for…

User-System Model(also: User-System Interaction Model)

A conceptual model that describes the relationship between a user and the technology system they interact with, taking into account the user's abilities, preferences, and needs alongside the system's capabilities, interfaces, and constraints. In accessibility engineering,…

Usher Syndrome(also: Usher's Syndrome)

A genetic condition that is the most common cause of combined deafness and blindness (deafblindness). It is characterized by sensorineural hearing loss present from birth and progressive vision loss from retinitis pigmentosa, which typically begins in adolescence or young…