The xylophone (from the Greek words ξύλον—xylon, "wood" + φωνή—phonē, "sound, voice", meaning "wooden sound") is a musical instrument in the percussion family that consists of wooden (not steel) bars struck by mallets. Each bar is an idiophone tuned to a pitch of a musical scale, whether pentatonic or heptatonic in the case of many African and Asian instruments, diatonic in many western children's instruments, or chromatic for orchestral use. The term may be used generally, to include all such instruments, such as the marimba and balafon or, more specifically, to refer to an orchestral instrument of somewhat higher pitch range than the chromatic marimba. It is sometimes mistakenly used to refer to the similar lithophone and metallophone, instruments of the glockenspiel or pixiphone type.

The semantron (Greek: σήμαντρον) or semanterion (σημαντήριον), also called a xylon (ξύλον) (Romanian: toacă; Russian: било, bilo; Bulgarian, Macedonian and Serbian: клепало, klepalo) is a percussion instrument used in monasteries to summon monks to prayer or at the start of a procession.