A choir is a musical ensemble of singers.
A body of singers who perform together as a group is called a choir or chorus. The former term is very often applied to groups affiliated with a church (whether or not they actually occupy the choir) and the second to groups that perform in theatres or concert halls, but this distinction is far from rigid. Choirs may sing without instrumental accompaniment, with the accompaniment of a piano or pipe organ, with a small ensemble (e.g., harpsichord, cello and double bass for a Baroque piece), or with a full orchestra of 70 to 100 musicians.
Most choirs are led by a conductor, who leads the performances with arm and face gestures.