In jazz ensembles, the instruments typically include wind instruments (one or more saxophones, trumpets, etc.), one or two chordal "comping" instruments (electric guitar, piano, or Hammond organ), a bass instrument (bass guitar or double bass), and a drummer or percussionist. Jazz ensembles may be solely instrumental, or they may consist of a group of instruments accompanying one or more singers. In rock and pop ensembles, usually called rock bands or pop bands, there are usually guitars and keyboards (piano, electric piano, Hammond organ, synthesizer, etc.), one or more singers, and a rhythm section made up of a bass guitar and drum kit.
Music ensembles typically have a leader. In jazz bands, rock and pop groups and similar ensembles, this is the band leader. In classical music, orchestras, concert bands and choirs are led by a conductor. In orchestra, the concertmaster (principal first violin player) is the instrumentalist leader of the orchestra. In orchestras, the individual sections also have leaders, typically called the "principal" of the section (e.g., the leader of the viola section is called the "principal viola"). Conductors are also used in jazz big bands and in some very large rock or pop ensembles (e.g., a rock concert that includes a string section, a horn section and a choir which are accompanying a rock band's performance).
In Western classical music, smaller ensembles are called chamber music ensembles. The terms duet, trio, quartet, quintet, sextet, septet, octet, nonet and dectet describe groups of two up to ten musicians, respectively. A group of eleven musicians, such as found in The Carnival of the Animals, is called either a hendectet or an undectet (see Latin numerical prefixes). A soloist playing unaccompanied (e.g., a pianist playing a solo piano piece or a cellist playing a Bach suite for unaccompanied cello) is not an ensemble because it only contains one musician.
A woodwind quartet usually features a flute, an oboe, a clarinet and a bassoon. A brass quartet features two trumpets, a trombone and a tuba. A saxophone quartet consists of a soprano saxophone, an alto saxophone, a tenor saxophone, and a baritone saxophone.
The string quintet is a common type of group. It is similar to the string quartet, but with an additional viola, cello, or more rarely, the addition of a double bass. Terms such as "piano quintet" or "clarinet quintet" frequently refer to a string quartet plus a fifth instrument. Mozart's Clarinet Quintet is similarly a piece written for an ensemble consisting of two violins, a viola, a cello and a clarinet, the last being the exceptional addition to a "normal" string quartet.
Some other quintets in classical music are the wind quintet, usually consisting of flute, oboe, clarinet, bassoon and horn; the brass quintet, consisting of two trumpets, one horn, a trombone and a tuba; and the reed quintet, consisting of an oboe, a soprano clarinet, a saxophone, a bass clarinet, and a bassoon.