Glossary
Terms used in accessibility research and practice. Each entry has a definition, common aliases, and category tags.
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- Z-Order(also: Stacking Order, Layer Order)
- Z-order refers to the front-to-back layering sequence of overlapping objects on a 2-D digital canvas, determining which objects appear in front of or behind others. In accessibility, Z-order is significant because screen readers in presentation software often read objects…
- Zancolli Classification(also: Zancolli Scale)
- A clinical classification system for residual upper-limb function after cervical spinal cord injury, developed by Argentine surgeon Eduardo Zancolli. The scale categorises hand and wrist function by the highest preserved motor level (C5, C6, C7, C8) and further subdivides C6 and…
- Zeigarnik Effect
- A psychological phenomenon identified by Bluma Zeigarnik in 1927 describing the tendency for people to remember interrupted or incomplete tasks better than completed ones. The effect explains why partially finished challenges, multi-level games, and serialized learning modules…
- Zernike Polynomials(also: Zernike Coefficients, Zernike Modes)
- A set of mathematical functions used to describe the shape of optical wavefronts, commonly employed in ophthalmology and optometry to characterise the optical aberrations of the human eye. Each Zernike polynomial represents a specific type of optical distortion — for example,…
- Zero-Knowledge Proof(also: ZKP, Zero-Knowledge Protocol)
- A zero-knowledge proof (ZKP) is a cryptographic method by which one party (the prover) can convince another party (the verifier) that a statement is true without revealing any information beyond the truth of the statement itself. For example, a voter can prove they are eligible…
- Zero-Shot Learning(also: Zero-Shot Prompting, Zero-Shot Inference)
- A machine-learning approach in which a model performs a task on classes or scenarios it has never seen explicit training examples for, relying entirely on its pre-trained knowledge and the structure of the prompt or input. In LLM-based accessibility testing, zero-shot prompting…
- Zero-Touch Interaction(also: Touchless Interaction, Hands-Free Interaction)
- An interaction paradigm that allows users to control devices or systems without physically touching them, typically through voice commands, gestures detected by cameras or sensors, or ambient sensing. Zero-touch interaction is particularly important for accessibility in contexts…
- ZigBee(also: IEEE 802.15.4)
- A low-power, low-data-rate wireless networking protocol based on the IEEE 802.15.4 standard, designed for short-range communication between devices in personal area networks. In accessibility and assistive technology contexts, ZigBee has been used in indoor navigation and…
- Zipf's Law
- A statistical observation that in any natural language corpus, the frequency of a word is inversely proportional to its rank in the frequency table. The most common word occurs roughly twice as often as the second most common, three times as often as the third, and so on. In…
- Zone of Proximal Development(also: ZPD)
- A concept from educational psychologist Lev Vygotsky describing the range of tasks that a learner can perform with the assistance of a more competent individual (scaffolding) but cannot yet perform independently. The ZPD lies between the zone of actual development (what the…
- Zoom Fatigue(also: Video Call Fatigue, Teleconference Fatigue)
- The exhaustion and mental strain experienced from prolonged use of video conferencing platforms, caused by the increased cognitive effort required to process non-verbal cues such as facial expressions, tone of voice, and body language through imperfect audiovisual technology.…
- Zoom Interface(also: Zoom Screen, Zoomable User Interface, ZUI)
- A user interface technique that allows users to magnify a portion of the screen to increase the effective size of interface elements, making them easier to select with low-precision pointing devices such as eye trackers or head mice. Unlike simple screen magnification for low…
- Zoom cycling(also: Zoom toggling, Magnification cycling)
- An interaction behaviour observed in screen magnifier users who frequently alternate between high magnification (to read fine details like axis labels and segment boundaries) and lower magnification (to see overall chart structure and make comparisons). Zoom cycling adds…
- ZoomText
- A commercial screen magnification and screen reading software for Windows, developed by Freedom Scientific (formerly Ai Squared). ZoomText provides up to 60x magnification along with features like smooth font display, cursor enhancements, focus tracking, and a built-in screen…
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