Broadly speaking, a chorus
is any substantial group of performers in a play
, revue, musical
who act more or less as one. It can also mean a work, or section of a work, performed by a chorus. Today, it is most usually used as a synonym for choir
to mean a group of singers
who all sing together or a piece sung by such a group, but it can also mean a group of dancers, and in Greek drama
it meant a group of actors
In colloquial usage, chorus is used to mean the refrain of a song.