a melody of some independence that accompanies another musical idea. Historically the term has meant that the obbligato part is "obligatory" and cannot be omitted (left out). The term is often used incorrectly to mean the opposite. In German it is spelled "Obligato".
(Ital.) : A part that must not be left out. Opp. is ad libitum . Popular parlance sometimes wrongly calls an optional line above the melody "the obbligato" (as in "Swanee River" + "Humoresque"). The better term here is "the discant."
an accompanying instrumental line in a vocal solo, which the player treats as a concerto