The Probert Encyclopaedia of Music

CHORUS

In music the term chorus is given to a company of singers singing in concert; and also to a composition of two or more parts, each of which is intended to be sung by a number of voices. The term chorus also describes the parts of a song or hymn that recur at intervals, as at the end of stanzas and also, a company of singers who join with the singer or choir in singer or choir in singing such parts.
Research Chorus