The deliberate use of animation in an interface: transitions between states, feedback on actions, loading behaviour, and the timing and easing that make them feel intentional.
Motion explains what just happened and where things came from, which reduces the mental work of using a product. Done badly it does the opposite — animation that delays a response makes a fast product feel slow.
We animate to communicate rather than to decorate, keep durations short, respect the reduced-motion setting for users who need it, and prototype the key transitions before building them.