1. A composition for three solo voices or instruments.
2. The middle movement of a minuet and trio or scherzo and trio form followed by a repeat of the first movement. The trio was originally composed for three voices but as more voices were added, the name of trio was retained.
3. The common term for the last strain (typically the third strain or third melody) of a march. The trio is typically repeated (once or twice) with some type of contrast between repeats and may contain melodic ideas from the previous strains. The contrasting devices can include dynamics (i.e. the first time soft and the repeat loud), contrast of timbres (i.e. the addition of instruments in each repeat), or contrast of texture (i.e. the addition of countermelodies or obbligatos in each repeat). The repeat of the trio is normally separated by a break strain or dogfight to provide a "break" from the melody and build excitement to the last repeat of the trio. This last repeat of the trio is often referred to as the grandioso because is is typically performed as the loudest and most majestic strain of the composition.
4. A group of three musicians who perform trios.

SUGGESTED LISTENING EXAMPLES:

Piano trio:
Mendelssohn: Piano Trio No. 2 in D minor, Op. 66, I

W. W. Norton - 4-CD Musical Example Bank -- Disc 2, Track 29

String trio:
Beethoven: Serenade in D major, Op. 8, I

W. W. Norton - 4-CD Musical Example Bank -- Disc 2, Track 28