Definitions:
a part of a song which is repeated after each verse

a large organized group of singers, especially one which performs with an orchestra or opera company

a simultaneous utterance of something by many people

(in ancient greek tragedy) a group of performers who comment together on the main action

a device used with an amplified musical instrument to give the impression that more than one instrument is being played

(of a group of people) say the same thing at the same time