A rhythm section is a group of musicians within a music ensemble or band that provides the underlying rhythm, harmony and pulse of the accompaniment, providing a rhythmic and harmonic reference and "beat" for the rest of the band. The rhythm section is often contrasted with the roles of other musicians in the band, such as the lead guitarist or lead vocals whose primary job is to carry the melody.

A musical ensemble, also known as a music group or musical group, is a group of people who perform instrumental and/or vocal music, with the ensemble typically known by a distinct name. Some music ensembles consist solely of instrumentalists, such as the jazz quartet or the orchestra. Other music ensembles consist solely of singers, such as choirs and doo-wop groups. In both popular music and classical music, there are ensembles in which both instrumentalists and singers perform, such as the rock band or the Baroque chamber group for basso continuo and one or more singers. In classical music, trios or quartets either blend the sounds of musical instrument families or group instruments from the same instrument family, such as string ensembles or wind ensembles. Some ensembles blend the sounds of a variety of instrument families, such as the orchestra, which uses a string section, brass instruments, woodwinds, and percussion instruments, or the concert band, which uses brass, woodwinds, and percussion.