hacky sack

Etymology
A trademark of. It uses reduplication of the word sack with the word hacky; a "hack", in the game's terminology, is akin to a point, and happens when every player in a group successfully passes the footbag.

Noun

 * 1)  A game or activity in which one or a group of players try to keep a footbag off the ground using only the feet.
 * 2)  The footbag used for such a game.