trios is a form of:

Trio



noun
1.
(a group of three, composition arranged for three voices or instruments) បទភ្លេងមានគ្រឿងបី, បទភ្លេងមានចម្រៀងបី, ប្រជុំមានវត្ដបី, ក្រុមមនុស្សបីនាក់
ENGLISH MEANING
noun
1.
The secondary, or episodical, movement of a minuet or scherzo, as in a sonata or symphony, or of a march, or of various dance forms; -- not limited to three parts or instruments.
2.
Three, considered collectively; three in company or acting together; a set of three; three united.
3.
A composition for three parts or three instruments.