noun pl. trios tri′os

1. any group of three persons or things
2. Music
   1. a composition for three voices or three instruments
   2. a group of three performers of such a composition, or any group of three musicians playing together
   3. the middle section of a minuet, scherzo, etc., orig. written in three voices, or parts

Etymology: Fr < It < tri-, tri-, as in duo, duo