Glossary

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High Contrast Mode(also: High Contrast, High Contrast Display)

An operating system or browser display setting that increases the visual distinction between foreground and background elements by using a limited colour palette with strongly contrasting colours, typically black and white or bright colours on dark backgrounds. High contrast…

Icon Size(also: Target Size, Touch Target Size)

The physical or rendered dimensions of graphical interface elements such as icons, buttons, and interactive controls. Research consistently shows that larger icon sizes improve interaction performance for users with low vision and motor impairments. WCAG 2.1 Success Criterion…

Image Accessibility(also: Visual Content Accessibility)

The practice of making images perceivable and understandable to people who cannot see them, primarily through alternative text descriptions. Image accessibility is a foundational requirement of WCAG (Success Criterion 1.1.1) and involves providing text alternatives that convey…

Image Description App(also: Visual assistance app, AI visual description app)

A smartphone or wearable application that captures an image of the user's surroundings and returns a spoken or textual description of its content, aimed primarily at blind and low-vision users. Early crowdsourced systems such as VizWiz (2010) relied on remote human workers;…

Instance-Level Recognition(also: Instance Recognition, Fine-Grained Recognition)

A computer vision task that involves distinguishing between specific individual objects within the same general category, rather than just identifying broad categories. For example, while category-level recognition might identify something as "a bag of chips," instance-level…

Large Print(also: Large Type, Enlarged Print, Giant Print)

Text or graphic material produced in a larger-than-standard font size to improve readability for people with low vision. Large print typically uses font sizes of 16 to 18 points or larger, though individual needs vary significantly depending on the type and degree of vision…

Lip-reading(also: Speechreading, Speech Reading, Visual Speech Perception)

The practice of understanding speech by visually interpreting the movements of the lips, face, and tongue, often used by deaf and hard-of-hearing individuals as a communication strategy. Lip-reading relies on watching the mouth region and facial expressions to decode spoken…

Luminance Contrast(also: Brightness Contrast)

The difference in perceived brightness between two adjacent surfaces or objects, as opposed to color contrast which involves differences in hue. Luminance contrast is particularly important for people with low vision, as many have difficulty distinguishing colors but can detect…

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 —…

Magnification Factor(also: Zoom Level, Magnification Level, Zoom Factor)

The ratio by which screen content is enlarged when using a screen magnifier. A magnification factor of 2x means the content appears twice its original size, but only one quarter of the original screen area is visible at any given time. Choosing an appropriate magnification…

Map Accessibility(also: Accessible maps)

The practice and field of making maps — digital geovisualizations, online navigation maps, tactile maps, and physical signage — perceivable, operable, understandable, and robust for users with disabilities. Map accessibility spans multiple modalities: tactile maps with raised…

Menu Selection(also: Menu Navigation, Menu Selection Task)

A fundamental computer interaction task in which a user chooses an option from a set of items presented in a menu structure, typically involving locating the target item, moving the cursor to it, and clicking to select. Menu selection performance is commonly measured by task…

Mouse Pointer(also: Cursor, Screen Pointer, Onscreen Pointer)

The small graphical indicator on a computer screen that represents the position of a pointing device such as a mouse, trackpad, or stylus. The mouse pointer is used to identify and interact with interface elements in graphical user interfaces through pointing, clicking, and…

Non-Visual Interaction(also: Non-Visual Access, Non-Visual Interface)

Methods of interacting with computer systems and digital content without relying on visual display. Non-visual interaction encompasses screen reader output, speech interfaces, keyboard navigation with audio feedback, braille displays, and haptic feedback. The Raman Principle…

Non-Visual Mental Model(also: Non-Visual Representation, Tactile Mental Model)

A cognitive representation of concepts, objects, or systems built through non-visual sensory channels — primarily touch, hearing, and proprioception — rather than through sight. People who are blind develop non-visual mental models that may differ structurally from visual models…

Non-Visual Navigation(also: Eyes-Free Navigation, Non-Visual Wayfinding)

Strategies and technologies that enable people who are blind or have low vision to navigate physical environments without relying on visual information. Non-visual navigation uses a combination of tactile cues (textured ground surfaces, cane feedback), auditory cues (traffic…

Non-Visual Reading(also: Audio Reading, Tactile Reading)

Methods of accessing written content without relying on visual perception, including braille reading, screen reader audio output, and text-to-speech technology. Non-visual reading is essential for blind users but presents unique challenges for navigation, skimming, and…

Non-visual Display(also: Nonvisual Display, Non-visual Interface)

A non-visual display presents information to a user through senses other than vision — most commonly hearing (synthesized speech, earcons, sonification), touch (Braille output, vibrotactile patterns, force-feedback haptics), or combinations thereof. Non-visual displays are…

Orthographic Projection(also: Parallel Projection)

A method of representing a three-dimensional object in two dimensions by projecting its features onto a flat plane using parallel lines perpendicular to that plane, eliminating perspective distortion. In accessibility contexts, orthographic projections (typically top, front, and…

Page Magnification(also: Page Zoom, Web Page Magnification)

An accessibility feature that enlarges the entire visual presentation of a web page, including text, images, and layout elements, to make content easier to see for people with low vision or visual fatigue. Unlike text-only size increases, page magnification scales all page…

Pattern Glare

A visual perceptual phenomenon where repeated striped or lined patterns cause discomfort, headaches, eyestrain, or visual distortions such as flickering, shimmering, or apparent movement. Pattern glare particularly affects people with dyslexia, epilepsy, and migraine, and can be…

Precompensation(also: Display Precompensation, Image Precompensation)

A technique in visual accessibility that pre-modifies displayed images in a way that is opposite to the optical distortion introduced by a user's eye, so that the image arriving at the retina more closely resembles the intended original. Precompensation works analogously to an…

Private Visual Content(also: PVC, Visual Privacy)

Private visual content (PVC) refers to visual information in images or videos that the person depicted or sharing the content considers private and would not want publicly disclosed. For people who are blind using visual interpreter services, PVC is a particular concern because…

Protanomaly(also: Protan Anomalous Trichromacy)

A type of colour vision deficiency where the long-wavelength (red) cone cells have a shifted sensitivity range rather than being absent entirely. Protanomaly is a milder form of protan CVD compared to protanopia, resulting in reduced but not absent ability to distinguish reds…

Protanopia(also: Protan Dichromacy, Red-Blind)

A type of colour vision deficiency caused by the complete absence of long-wavelength (red) cone cells in the retina. People with protanopia cannot distinguish between red and green and perceive reds as significantly darker than people with typical colour vision. This darkening…

Redundant Encoding(also: Redundant Coding, Multi-Channel Encoding)

A design principle that communicates information through multiple visual channels simultaneously — such as colour plus shape, pattern, text label, or position — so that no single channel is required for comprehension. Redundant encoding is a foundational recommendation for CVD…

Relative Font Sizing(also: Relative Units, Scalable Typography, Flexible Font Sizes)

The practice of specifying text sizes using relative units (such as em, rem, or percentages) rather than absolute units (such as pixels or points), allowing text to scale when users adjust their browser or system font size settings. Relative font sizing is an important…

Remote Assistance(also: Remote Sighted Assistance, Visual Interpreting)

A service model where people who are blind or have low vision connect with sighted volunteers or trained agents via a live video call to receive real-time visual descriptions and guidance. Services like Be My Eyes and Aira use smartphone cameras to share the user's environment…

STEM Accessibility(also: Accessible STEM, STEM for Students with Disabilities)

The design and delivery of science, technology, engineering, and mathematics education in ways that are accessible to students with disabilities. STEM accessibility is a particularly acute challenge for students with vision impairments, as STEM subjects heavily rely on visual…

School for the Blind(also: Blind School, Residential Blind School)

A specialized educational institution that serves students with vision impairments, often as a residential facility where students live on campus. In India and other Global South countries, schools for the blind are frequently underfunded, teacher-constrained, and reliant on…

Scotopic Sensitivity Syndrome(also: Irlen Syndrome, Visual Stress, Meares-Irlen Syndrome)

A perceptual processing condition in which the brain has difficulty handling certain visual information, particularly high-contrast patterns like black text on a bright white background. People with scotopic sensitivity may experience text appearing to move, shimmer, or blur on…

Screen Magnification(also: Screen Magnifier, Display Magnification)

Software or operating system features that enlarge a portion of the screen content to make it readable for people with low vision. Common modalities include full-screen magnification (which expands the entire display around a movable center point) and lens magnification (which…

Screen Magnifier(also: Screen Magnification Software, Magnification Software)

An assistive technology application that enlarges a portion of the screen display to make content more readable for people with low vision. Screen magnifiers work by rendering a zoomed-in view of the area around the cursor or focus point, often providing additional features such…

Screen Reader(also: Screen Reading Software)

An assistive technology application that converts digital text and interface elements into synthesized speech or braille output, enabling people who are blind or have low vision to interact with computers, smartphones, and other digital devices. Screen readers interpret the…

Screen Reader Output(also: Screen Reader Speech)

The audio or braille output generated by screen reader software as it interprets and conveys on-screen content to blind and low vision users. Screen reader output quality significantly impacts reading comprehension and efficiency, as the linearization of visual content into…

Shoreline Technique(also: Trailing, Edge Following)

An orientation and mobility technique used by people who are blind or have low vision in which the traveler follows a consistent edge or boundary — such as the edge of a sidewalk, a wall, a fence line, or the border between grass and pavement — to maintain orientation and stay…

Shoulder Surfing

A form of visual eavesdropping where an attacker observes a person entering sensitive information such as passwords, PINs, or personal data by looking over their shoulder or from a nearby vantage point. Shoulder surfing is a particularly significant security concern for people…

Simulation Glasses(also: Cataract Glasses, Vision Simulation Glasses, Low-Vision Simulation Goggles)

Simulation glasses are wearable lenses or goggles that reproduce the functional visual experience of specific eye conditions — cataracts, macular degeneration, glaucoma, hemianopia, and others — by blurring, smearing, adding central scotomas, or restricting the field of view.…

Situational Visual Impairment(also: SVI, Situational Visual Impairments)

A temporary reduction in a person's effective vision or reading performance caused by the environment or context rather than by a medical condition. Common examples include trying to read a phone screen in bright sunlight, while walking or on a moving vehicle, in low light, or…

Spatial Learning(also: Spatial Cognition, Environmental Learning)

The process of acquiring and integrating information about an environment into cognitive maps — mental representations of spatial relationships between places, paths, and landmarks. For sighted individuals, spatial learning occurs largely through casual visual observation. For…

Tactile Aid(also: Tactile Learning Aid, Tactile Tool)

A physical object designed to convey information through touch, used to make visual or abstract concepts accessible to people who are blind or have low vision. Tactile aids can include raised-line drawings, textured surfaces, 3D-printed models, and laser-cut representations of…

Tactile Diagram(also: Raised Diagram, Embossed Diagram)

A diagram rendered in a tactile format that can be explored through touch, typically using raised lines, textures, and Braille labels on special paper or thermoform plastic. Tactile diagrams are essential for teaching STEM concepts to students with vision impairments,…

Tactile Exhibit(also: Touch Exhibit, Hands-On Exhibit, Tactile Display)

A museum or gallery exhibit designed to be explored through touch rather than sight, allowing visitors to physically interact with objects, models, or replicas. Tactile exhibits are particularly important for accessibility as they enable blind and low-vision visitors to…

Tactile Image(also: Tactile Graphic, Tactile Picture, Touch Image)

A tactile image is a raised or textured representation of a visual image designed to be perceived through touch rather than sight. Tactile images can be produced through various methods including embossing, swell paper (microcapsule paper), Braille printers, thermoforming, and…

Tactile Learning Material(also: Tactile Teaching Aid, Hands-On Learning Material)

Physical educational materials designed to be explored through touch, enabling students with vision impairments to understand concepts that are typically presented visually. Tactile learning materials include raised-line diagrams, 3D models, textured maps, manipulable math…

Tactile Markers(also: Bump Dots, Tactile Labels, Braille Labels)

Physical indicators such as raised dots, textured stickers, or braille labels applied to objects, appliances, and controls to make them identifiable by touch for people who are blind or have low vision. Tactile markers are commonly placed on oven dials, microwave buttons,…

Teachable Object Recognizer(also: Teachable Machine, Personalized Object Recognizer)

A machine learning application that allows end users to train custom object recognition models by providing their own example images, rather than relying on pre-trained models with fixed categories. In accessibility contexts, teachable object recognizers empower blind and…

Teacher with Vision Impairment(also: TVI, Visually Impaired Teacher, Blind Teacher)

An educator who is blind or has low vision and teaches in educational settings, often in schools for the blind where they share the lived experience of their students. TVIs are particularly prominent in the Global South, where residential schools for the blind employ significant…

Text Modification(also: Text Formatting, Text Presentation Modification)

Changes to the visual presentation or formatting of text to improve readability without altering the actual content. Text modifications include adjustments to font type, size, color, spacing, line height, background color, text alignment, and column width. Research with people…

Text Reflow(also: Content Reflow, Responsive Text)

The ability of text content to rearrange and wrap within its container when the viewport is resized or text is zoomed, so that users can read without horizontal scrolling. Text reflow is essential for users with low vision who magnify content, as well as for mobile users on…