a cappella | en

A cappella (Italian for "From the chapel/choir") music is vocal music or singing without instrumental accompaniment, or a piece intended to be performed in this way. In modern usage, a cappella often refers to an all-vocal performance of any style, including barbershop, doo wop, and modern pop/rock.

The term is also sometimes applied to vocal music that is accompanied only by drums or percussion.

Other spelling variants: http://www.singers.com/a-cappella.html .