Spacing is the distance an element travels between two frames of an animation.
By increasing and decreasing the spacings over the course of multiple frames, Easing describes how softly a motion starts and ends through acceleration and deceleration. This is achieved by graduadl... More can be added to a motion.
A motion with the same spacing between each frame is called a linear motion. This only occurs very rarely in nature and usually needs to be avoided.
Spacing is one of the 12 principles of animation.