Trio (music)

Group of three musicians
the musical term

In music, a trio (from the Italian) is any of the following:
a composition for three performers or three musical parts
in larger works, the middle section of a ternary form (so named because of the 17th century practice of scoring the contrasting second or middle dance appearing between two statements of a principal dance for three instruments)
an ensemble of three instruments or voices performing trio compositions.

A trio is a composition for three performers or musical parts. Works include Baroque trio sonatas, choral works for three parts, and works for three instruments such as string trios. In the trio sonata, a popular genre of the 17th and early 18th century, two melodic instruments are accompanied by a basso continuo, making three parts in all. But because the basso continuo is usually played by two instruments (typically a cello or bass viol and a keyboard instrument such as the harpsichord), performances of trio sonatas typically involve four musicians. However there are also examples for a single performer such as Bach's Organ Sonatas or Trios, BWV 525–30 for two hands and a pair of feet, and also for two performers, such as his Violin Sonatas, Viol Sonatas and Flute Sonata, in which the harpsichordist's right hand performs a melodic part. In vocal music with or without accompaniment, the term terzet is sometimes preferred to "trio".

From the 17th century onward, trio has been used to describe a contrasting second or middle dance appearing between two statements of a principal dance, such as a minuet or bourrée. This second dance was originally called a trio because of the 17th century practice of scoring it for three instruments, and later examples continued to be referred to as trios, even when they involved a larger number of parts. The Menuet of Bach's Brandenburg Concerto No. 1 (1721) is a late nod to the original practice, with trios for two oboes and bassoon as well as two horns and a third part played by three oboes in unison.