A choir singing without instrumental accompaniment is called an a cappella choir. Non-accompanied vocal music is considered a cappella due to restrictions on the use of instruments in medieval churches.
Many standard choral works are a cappella in that no accompaniment is written in except perhaps for rehearsal purposes. But in the modern parlance, it applies to vocal performers who disdain instrumental accompaniment in all cases. A cappella music attained renewed prominence in the 1980s and 1990s, spurred by the success of songs by popular recording artists such as Bobby McFerrin and Boyz II Men. Barbershop, doo wop, and contemporary a cappella are some of the major movements within modern a cappella musicmaking.
Arrangements of popular music for small a cappella ensembles usually include one voice singing the lead melody, one singing a rhythmic bass line, and the remaining voices contributing chordal accompaniment (In Japan, these parts are known as vocal, bass, and chorus, respectively). However, many contemporary a cappella groups have adopted other approaches, including polyphonic treatments and "human beatbox" effects. A cappella can also describe the practice of using just the vocal track(s) from a multitrack recording to either remix or put onto vinyl records for DJ's.
Famous a cappella ensembles: