four-part harmony

The term "four-part harmony" refers to music written for four voices, or four musical instruments, or a keyboard instrument, or some other medium, where the various parts give a different note of each chord of the music. Typically, the first of the four parts will sing (or play) the melody, with the other three parts providing the supporting harmonies. It is unusual for any of the four parts to share the same pitch, although it happens at times.