Sagging buttocks is a deflation in the area, with the surrounding skin appearing loose and slack.
Sagging buttocks are generally caused by a lack of definition in the gluteus maximus, the largest muscle in the area. The area can also hold stubborn fat, especially in women where the female hormone oestrogen causes fat to be distributed in the buttocks and thighs. This is as opposed to men where the fat is stored in the stomach area.
Sagging buttocks can incur with excessive weight gain or loss, as well as be a result of the ageing process. The skin around the area can also experience sagging due to a loss of elasticity in the skin, giving a wrinkled and stretched appearance.