A discant (occasionally, particularly later, written descant) is a form of medieval music in which one singer sang a fixed melody, and others accompanied with improvisations.
Later on, the term came to mean, the treble or soprano singer in any group of voices, or the higher pitched line in a song, and eventually, by the Renaissance, referred generally to counterpoint.
Descant can also refer to the highest pitched of a group of instruments, particularly the descant viol or recorder.