trio
n pl , trios
1 a group of three people or things
a a group of three singers or instrumentalists or a piece of music composed for such a group
b a subordinate section in a scherzo, minuet, etc., that is contrastive in style and often in a related key
3 (Piquet) three cards of the same rank (C18: from Italian, ultimately from Latin tres three; compare duo)
piano trio
n
1 an instrumental ensemble consisting of a piano, a violin, and a cello
2 a piece of music written for such an ensemble, usually having the form and commonest features of a sonata
trio sonata
n
1 a type of baroque composition in several movements scored for two upper parts and a bass part
2 a similar type of composition played on a keyboard instrument, esp. an organ