Gamelan is a traditional Indonesian orchestra, mainly made up of percussion instruments, which are played by striking them. The main instruments are metal gongs. Other instruments include double-ended drums to mark the rhythm, xylophones for convex metal or wooden keys, rebabs (bowed lutes played like cellos), and flutes. Gamelan orchestras vary in size and composition. They generally accompany dancing or wayang (shadow theater) performances. Individual singers and a chorus normally sing with the orchestra. A full gamelan consists of about 20 performers, but most orchestras have fewer.