concertino
In classical music, a short concerto or the group of solo instruments in a concerto grosso.
The concertino of the Baroque period is characterized by the contrast between the solo instrument group and the ripieno.
協奏曲 is a full concerto, while 小協奏曲 is a shorter or smaller-scale concerto, or the solo group in a concerto grosso.
Compound of 小 (small) and 協奏曲 (concerto), likely a calque from Italian 'concertino'.