SEMI BALANCE BALL  

GEER balance ball was called as bosu ball, bosu balance trainer, balance ball chair, bosu ball abs, half exercise ball, half yoga ball.  it's like an exercise ball that's been cut in half with a platform on the bottom. You can use it dome-side-up almost like a step and stand on it, sit on it, lie down on it or bounce around on it for cardio, lower body strength, or core moves.