Acousmatic music (from Greek ἄκουσμα akousma, "a thing heard") is a form of electroacoustic music that is specifically composed for presentation using speakers, as opposed to a live performance. It stems from a compositional tradition that dates back to the introduction of musique concrète in the late 1940s. Unlike musical works that are realised using sheet music exclusively, compositions that are purely acousmatic (in listening terms) often exist solely as audio recordings, also referred to as fixed media.