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.
The core elements of the rhythm section are usually the drum kit and bass. The drums and bass provide the basic pulse and groove of a song.
The section is augmented by other instruments such as keyboard instruments and guitars that are used to play the chord progression upon which the song is based.
The bass instrument (either double bass or electric bass guitar, or another low-register instrument, such as synth bass, depending on the group and its style of music) plays the low-pitched bassline. The bassline is a musical part that supports the chord progression, typically by playing a musically interesting bassline that outlines the important notes of the harmony, often by emphasizing the root, fifth, and third of each chord.
The term is common in modern small musical ensembles, such as bands that play jazz, country, blues, and rock. Orchestras that play popular music, film soundtracks (often called a "pops orchestra"), or musical theatre orchestras may also feature a rhythm section (at a minimum drum kit and electric bass/amplified double bass, but possibly including keyboards and guitar) that performs with the larger ensemble. The rhythm section provides a rock or pop feel and sounds that would be difficult to recreate with orchestral instruments.
A typical rhythm section comprises one or more guitars (either electric guitars, in rock music bands; acoustic guitars, in country music, folk music and blues or both electric and acoustic in some bands); and/or a keyboard instrument (piano, electric piano, Hammond organ, synthesizer, etc.) a double bass or electric bass guitar (depending on the style of music), and drums (usually acoustic, but in some post-1980s styles, the drums may be electronic drums).