# Glossary

> Every interanimate term, defined in one place.

**Acknowledgment** — The first visible response to an input, delivered on input start within the response budget.

**Bounce** — The perceptual spring parameter controlling overshoot. 0 is critically damped (no overshoot); positive values overshoot; negative values are overdamped. Set via the *character* token.

**Channel** — The classification of a value. **Spatial** channels (position, size, scale, rotation, shape) default to springs; **effect** channels (opacity, color, blur, shadow) default to tweens.

**Character** — Token scale for how much a spring overshoots: `flat`, `smooth`, `lively`, `bouncy`.

**Choreography** — The rules governing how multiple motions relate in space and time: origins, relationships, ordering, staggering, symmetry.

**Commit** — The point at which an interaction's outcome is performed (a press activates; a drag decides to dismiss).

**Decay** — A motion that coasts from current velocity to rest, slowing continuously, with no target. Used for momentum and for projection.

**Direction locking** — Deciding a drag's axis at the hysteresis threshold and holding it, so perpendicular movement goes to another owner (usually scroll).

**Effect channel** — See *Channel*.

**Environment** — Context that affects resolution: input modality, hover availability, device capability, performance headroom.

**Essential motion** — Motion that *is* the information or function, so removing it would change what the content means or does. Direct manipulation is essential. Exempt from reduced-motion substitution.

**Frequency** — Token scale for how often a person encounters a motion: `constant`, `frequent`, `occasional`, `rare`. Caps tempo and character.

**Gesture lifecycle** — The shared sequence of states every interaction follows: Rest, Engaged, Tracking, Released, Committed, Settling, Cancelled.

**Grab offset** — The distance between where the input touched an object and the object's own reference point, preserved throughout an interaction.

**Hand-off** — The transfer of a value's ownership between an interaction and a motion (or between two motions), always carrying presentation value and velocity.

**Hysteresis** — A small movement threshold an input must cross before it commits to being a drag.

**Intent** — A declaration of what a moment means (`acknowledge`, `reveal`, `navigate`…), which resolves to purpose, channels, motion, tokens, choreography, and reduced behavior.

**Interaction** — A person directly controlling values through input. One of the two kinds of value owner.

**Interruption** — New input or a new target arriving while a motion is in flight. Always allowed; always continuous.

**Motion** — A behavior that moves a value without a person's direct control: spring, decay, or tween. One of the two kinds of value owner.

**Origin** — The place a revealed, concealed, navigated, or morphing element is spatially connected to: a trigger, an edge, itself, or a shared element.

**Owner** — The single motion or interaction controlling a value at a given instant.

**Perceptually complete** — The moment a motion *looks* finished. Follow-up UI may react here. Contrast with *settled*.

**Preference** — What the person has asked for, chiefly motion preference (full or reduced). Resolved last; never overridden.

**Presentation value** — What a value is on screen right now, as opposed to its target.

**Projection** — Using release velocity and decay to predict where a gesture was heading, and choosing the outcome from that prediction.

**Purpose** — Why a motion exists: feedback, orientation, state, attention, or delight. Every motion has exactly one primary purpose.

**Reduced behavior** — The substitution an intent uses when the person prefers reduced motion. Required for every intent.

**Resistance** — Progressive damping of movement past a boundary (rubber-banding).

**Resolution** — The fixed-order process (intent → author → frequency → environment → preference) that turns an intent into concrete motions. Each step can only reduce.

**Retarget** — Changing a motion's target while it's in flight, without resetting its velocity.

**Settled** — A value within a negligible threshold of its target with effectively zero velocity. Ownership and resources are released here. Nothing a person waits on is tied to settling.

**Spatial channel** — See *Channel*.

**Spring** — A motion that moves a value toward a target, respecting current velocity, described by perceptual duration and bounce. The default for spatial channels.

**Stagger** — Small, capped offsets between the starts of motions in a group. Decorative; never delays interactivity.

**Tempo** — Token scale for how long a motion feels: `instant`, `swift`, `quick`, `standard`, `relaxed`, `deliberate`.

**Tween** — A motion along a fixed easing curve over a fixed duration. The default for effect channels.

**Value** — Any continuously changing quantity that affects what's on screen. Has a presentation value, velocity, target, and owner.

**Velocity** — How fast and in which direction a value is changing. Always carried through hand-offs.