In music, a song is a composition for voice or voices, performed by singing. A song may be accompanied bymusical instruments, or it may be unaccompanied, as in the case of a cappella songs. The lyrics (words) of songs are typically of a poetic, rhyming nature, though they may be religious verses or free prose.

A song may be for a solo singer, a duet, trio, or larger ensemble involving more voices. Songs with more than one voice to a part are considered choral works. Songs can be broadly divided into many different forms, depending on the criteria used. One division is between "art songs", "pop songs", and "folk songs". Other common methods ofclassification are by purpose (sacred vs secular), by style(dance, ballad, Lied, etc.), or by time of origin (Renaissance, Contemporary, etc.).