Wording.

Easing

A curve that controls how an animation accelerates and decelerates over time, rather than moving at a constant rate.

Example usage
Use ease-out for elements entering the screen — they should arrive quickly and settle softly.
Editor’s note

Linear motion looks mechanical. Almost every UI animation benefits from easing. The most common mistake is applying ease-in where ease-out is needed — elements should decelerate as they arrive, not accelerate.