An indoor percussion ensemble or indoor drumline consists of the marching percussion (or battery) and front ensemble (pit or frontline) sections of a marching band or drum corps. The only exceptions are in concert divisions (e.g. Percussion Scholastic Concert Open) where the marching line is absent and the ensemble consists entirely of a pit. Indoor percussion marries elements of music performance, marching, and theater; thus, the activity is often referred to as percussion theater. Although most indoor percussion ensembles are affiliated with high schools, there are also many independent groups that draw participants from a large area. Independent groups typically start rehearsing in October, while high school groups typically start after their fall marching band season ends. Because of this, the activity is often called winter percussion or winterline.