in music, 18th-century genre for orchestra or small ensemble that was written in several short movements. It was akin to the 18th-century serenade and divertimento and, like these, was often intended for performance outdoors.

The designation seems to have referred more to the intended function than to the precise nature of the work and seems as well to have been somewhat interchangeable with various other terms, including not only serenade and divertimento but also notturno, serenata (also used for short operatic works), and Finalmusik. Among suggested origins of the term are the Italian cassa, “drum” (Mozart's cassations K 63 and 99 open with march movements), and the Austrian dialectal gassatim gehen, “to go into the street.” Although the term is used occasionally by Haydn and Mozart and occurs in early listings of their music, it had fallen into disuse by the end of the 18th century.