Tuck Position: A gymnastics body position where the knees and hips are bent and drawn into the chest with the hands holding the knees. This body position is used in somersaults to rotate faster. Variation on the tuck position include the open tuck and cowboy tuck positions.

Triple Back Tuck by Valeri Liukin

(Nastia Liukin’s father and coach)

Actually, you might better describe this somersault position as a cowboy tuck.