During the (transverse) abduction of the hip we target the three muscles of the butt, which are collectively referred to as the glutes (short for "gluteus") by most athletes. These three muscles are the gluteus maximus, gluteus medius and the gluteus minimus.
The largest of these muscles is the gluteus maximum, which makes up the bulk of the backside. This muscle is extremely thick and powerful, and we recruit it during the extension of the hip (such as during the deadlift). The other two muscles are located to the outer region of the butt and are mainly responsible for hip abduction and rotation.