Eases, bouncing either at the beginning (easeIn), the end (easeOut), or both (easeInOut). Bounce is a convenience class that congregates the 3 types of Bounce eases (BounceIn, BounceOut, and BounceInOut) as static properties so that they can be referenced using the standard synatax, like Bounce.easeIn, Bounce.easeOut, and Bounce.easeInOut.
GreenSock Docs (HTML5/JS)
Bounce
Properties
easeIn : BounceIn
[static] Bounces slightly at first, then to a greater degree over time, accelerating as the ease progresses.
easeInOut : BounceInOut
[static] Bounces in increasing degree towards the center of the ease, then eases out, bouncing to the end (decreasing in degree at the end).
easeOut : BounceOut
[static] Eases out, bouncing at the end.