Gamelan refers to the traditional Indonesian percussion orchestra and its instruments. The main instruments are hand-forged percussive instruments, including xylophones, gongs, gong-chimes, drums, cymbals, string instruments, and bamboo flutes. Gamelan music follows a strict set of rules and techniques regarding tuning, layout, rhythmic and metric patterns, and performance. Typically, a melody is played simultaneously by several instruments, and multiple instruments may play interlocking parts to form a single rhythm. This is typically played for religious rituals and ceremonies, traditional theater, festivals, and concerts, by men, women, and children of all ages. It is also used for music therapy and is seen as an expression of human feeling and a connection to the universe. It is an integral part of Indonesian identity for thousands of years, dating back as far as the eighth-century relief sculptures of the Borobudur temple. Gamelan is practiced by vocalists, instrumentalists, instrument makers, and tuners. It continues to be passed down from generation to generation through both formal and informal education, including classrooms and after-school activities. Gamelan has been an influential part of Indonesian culture. Although it is played in many parts of Indonesia such as in Sumatra, Kalimantan, and West Nusa Tenggara, it is mostly known and practiced in Java and Bali.