The King's Singers, Affabre Concinui) or musical instrument groups, but can be applied to any situation where six similar or related objects are considered a single unit.
Many musical compositions are named for the number of musicians for which they are written.
Steve Reich's "Sextet", for example, is written for six percussionists.
In jazz music a sextet is any group of six players, usually containing a drum set (bass drum, snare drum, hi-hat, ride cymbal), string bass or electric bass, piano, and various combinations of the following or other instruments: guitar, trumpet, saxophone, clarinet, trombone.
In heavy metal and rock music, a sextet typically contains, but is not restricted to, a lead vocalist, two guitarists, a bassist, drummer, and keyboardist.