FOURPARTHARMONY
Four-part harmony
The term "four-part harmony" refers to music written for four voices, or four musical instruments, where the various parts give a different note of each chord of the music. Typically, the first of the four parts will sing the melody, with the other three parts providing the supporting harmonies. It is unusual for any of the four parts to share the same note, although it happens at times.The above text is a snippet from Wikipedia: Four-part harmony
and as such is available under the Creative Commons Attribution/Share-Alike License.