a part of the score that must be performed without change or omission

an optional instrumental part above the melody

A second part or accompaniment to solo parts

An elaborate melodic part accompanying a solo or principal melody.

(ah-blee-GAH-toe) The proper Italian term for what we would more generally call a "descant"; a melodic line that complements the general tune, usually sung or played in a higher register.

An accompanying part that is very important and thus not to be omitted; countermelody.

In classical music an obbligato (Italian for obligatory, from Latin word obligare, to oblige) is an elaborate accompaniment part played by a single instrument. Originally indicated a passage of music that was to be played as written, without changes or omissions, as opposed to ad libitum.