A septet is a formation containing exactly seven members. It is commonly associated with musical groups, but can be applied to any situation where seven similar or related objects are considered a single unit, such as a seven-line stanza of poetry.
In jazz music a septet is any group of seven players, usually containing a drum set, string bass or electric bass, and groups of one or two of the following instruments, guitar, piano, trumpet, saxophone, clarinet, or trombone.
One of the most famous classical septets is the Septet in E-flat major, Op. 20, by Ludwig van Beethoven, composed around 1799–1800, for clarinet, bassoon, horn, violin, viola, cello, and double bass. The popularity of Beethoven's septet made its combination of instruments a standard for subsequent composers, including Conradin Kreutzer (Op. 62, 1822), Franz Berwald, and Adolphe Blanc (Op. 40, ca. 1864), and, with small changes in the instrumentation, Franz Lachner (1824), and Max Bruch (1849). When Franz Schubert added a second violin in 1824 for his Octet, he created a standard octet that influenced many other subsequent composers (Kube 2001). The Septet in E-flat major, Op. 65, for trumpet, piano, string quartet, and double bass by Camille Saint-Saëns from 1881 is one of that composer's works. The modern composer Bohuslav Martinů wrote three septets: a group of six dances called Les Rondes for oboe, clarinet, bassoon, trumpet, two violins, and piano (1930); a piece called Serenade No. 3 for oboe, clarinet, four violins, and cello (1932); and a Fantasie for theremin, oboe, piano, and string quartet (1944). Darius Milhaud composed a String Septet in 1964 for string sextet and double bass. Paul Hindemith composed a wind septet in 1948 for flute, oboe, clarinet, bass clarinet, bassoon, horn, and trumpet. Hanns Eisler composed two septets, both scored for flute, clarinet, bassoon, and string quartet: Septet No. 1 Op. 92a ("Variations on American Children's Songs") (1941), and Septet No. 2 ("Circus") (1947), after Chaplin’s 1928 movie The Circus. Two component works in the series of Chôros by the Brazilian composer Heitor Villa-Lobos are scored for seven instruments: No. 3 (1925), subtitled "Pica-páo" (Woodpecker), is for clarinet, bassoon, saxophone, 3 horns, and trombone (or for male chorus, or for both together), and No. 7 (1924), actually subtitled "Septet", is for flute, oboe, clarinet, saxophone, bassoon, violin, and cello (with tam-tam ad lib.).
There are many 20th-century works for seven instruments for which it is uncertain whether the term "septet" should be used, since they may not obviously be chamber music or have titles indicating otherwise. Examples include Maurice Ravel's Introduction and Allegro (1905), Rudi Stephan's Music for Seven String Instruments (1911), Leoš Janáček's Concertino (1925), Arnold Schoenberg's Suite, Op. 29 (1925–26), Isang Yun's Music for Seven Instruments (1959), Aribert Reimann's Reflexionen (1966), and Dieter Schnebel's In motu proprio canon for seven instruments of the same kind (1975) (Kube 2001).
The dictionary definition of septet at Wiktionary