An accompaniment is the musical part which supports (or accompanies) the main melody or theme of a piece of music. This might involve harmonic and/or rhythmic support, i.e. providing the “beat” for the music!

The accompaniment might be played by a single musician. For example, a solo vocal piece might be accompanied by a guitar or piano. Accompaniment can also be played by a whole musical ensemble, such as a Big Band in jazz or a pit orchestra in musical theatre.