Overshoot inserts two in-between keyframes—an anticipation and an overshoot—between every pair of selected keyframes on your F-Curves. Anticipation moves slightly backward from the start value before the main motion, and overshoot pushes beyond the end value for a snappy finish.

Redo Panel
Target
Sets the target F-Curves, Selected Keyframes or timeline Playback Range for the operation.
Anticipation %
How far backward, as a percentage of the total delta, to place the anticipation key after the first keyframe.
Overshoot %
How far beyond the end value, as a percentage of the delta, to place the overshoot key before the next keyframe.
Anticipation Offset
Number of frames added after the first keyframe at which the anticipation key is inserted.
Overshoot Offset
Number of frames before the next keyframe at which the overshoot key is inserted.