Which of these is a musical ensemble consisting of eight instruments or voices?

In music, an octet is a musical ensemble consisting of eight instruments or voices, or a musical composition written for such an ensemble.

Octets in classical music are one of the largest groupings of chamber music. Although eight-part scoring was fairly common for serenades and divertimenti in the 18th century, the word "octet" only first appeared at the beginning of the 19th century, as the title of a composition by Prince Louis Ferdinand of Prussia, whose Octet Op. 12 (published posthumously in 1808) features the piano, together with clarinet, 2 horns, 2 violins, and 2 cellos. Later octets with piano were written by Ferdinand Ries (Op. 128, 1818, with clarinet, horn, bassoon, violin, viola, cello, and double bass), Anton Rubinstein (Op. 9, 1856, with flute, clarinet, horn, violin, viola, cello, and double bass), and Paul Juon (Chamber Symphony, Op. 27, 1907) (Kube 2001).

Jazz ensembles of eight players will frequently be termed an octet. These ensembles may be for any combination of instruments, but the most common line-up is trumpet, alto sax, tenor sax, trombone, guitar, piano, bass and drums, with guitar occasionally making way for another horn, for example baritone sax. The Jamil Sheriff Octet is an example of a classic octet. Ornette Coleman's ensemble for the Free Jazz album (referred to as a double quartet) is an example of two quartets playing together at the same time.