A somersault is a gymnastic move in which you lower your head almost to the floor and roll forward so your feet flip over your head. Fancier somersaults are done in the air, rather than on the ground.
There are many types of somersaults—forward, backward, and sideways, among other variations. In gymnastics, a somersault on the floor is more often called a roll. The word somersault, which works as a verb too, comes from the now-obsolete French sombresault, from the Latin roots supra, "over," and saut, "a jump."