Glossary

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Target Expansion(also: Expanding Targets, Dynamic Target Sizing)

An interaction technique where clickable interface elements dynamically grow in size as the cursor approaches, making them easier to select while conserving screen space when not being targeted. Research shows target expansion can reduce selection times by up to 14% and error…

Target Selection(also: Target Acquisition, Pointing)

The fundamental interaction task of moving a cursor or pointer to a specific location on screen and confirming selection, such as clicking a button or link. Target selection difficulty is affected by target size, distance to target, and user motor abilities—relationships…

Target Size(also: Touch Target Size, Click Target Size, Hit Area)

The physical dimensions of an interactive element on screen — such as a link, button, or checkbox — that a user must point to and activate. Adequate target size is critical for users with motor impairments, tremor, or limited dexterity, as small targets require greater precision…

Target acquisition(also: Target selection, Pointing task)

The process of moving a pointer or input device to a specific on-screen element and selecting it, such as tapping an icon, clicking a button, or choosing a menu item. Target acquisition is a fundamental interaction in graphical user interfaces, and its difficulty is influenced…

Target-Based Navigation(also: Target-Based Cursor Control, Object-Based Navigation)

A cursor control method where users identify the desired destination directly by name or label, such as saying "Select Friday" to move the cursor to that word on screen. Target-based navigation can be efficient when targets are clearly identifiable, but becomes error-prone as…

Tetraplegia(also: Quadriplegia)

A condition resulting from injury to the cervical (neck) portion of the spinal cord, causing partial or complete loss of motor function and sensation in all four limbs as well as the trunk. The extent of impairment varies depending on the level and completeness of the injury,…

Touch Accessibility(also: Touchscreen Accessibility)

The design and adaptation of touch-based interfaces to be usable by people with diverse motor, sensory, and cognitive abilities. Touch accessibility addresses challenges including insufficient target sizes for users with limited fine motor control, lack of alternatives to…

Touch Drift(also: Finger Drift)

The displacement of a finger's contact point on a touchscreen between the initial finger-down position and the final finger-up position during a single touch interaction. Touch drift measures how far a touch "slides" from where it started to where it ended, distinct from touch…

Touch target(also: Tap target, Touch target size, Target size)

The interactive area on a touchscreen or pen-based display that responds to user input when tapped or pressed. Touch target size is a critical accessibility consideration because targets that are too small or too closely spaced cause selection errors, particularly for older…

Trackball

A trackball is a pointing device consisting of a ball housed in a stationary socket that the user rotates to move the on-screen cursor, with buttons nearby for clicking. Unlike a mouse, a trackball does not require arm movement across a surface, making it valuable for people…

Tremor(also: Hand Tremor, Essential Tremor)

An involuntary, rhythmic shaking movement of one or more parts of the body, most commonly affecting the hands. Tremor can result from various conditions including essential tremor, Parkinson's disease, multiple sclerosis, stroke, or medication side effects, and its severity can…

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