Chorus

The source of picture:
http://chorus-nnsu.ru/images/chorus.jpg

Chorus: noun [countable] verb [transitive]
Definition:
noun
1. the part of a song that is repeated after each EVRSE.
2. a large group of people who sing together [= choir].
3. a piece of music written to be sung by a large group of people.
4. a group of singers, dancers, or actors who act together in a show but do not have the main parts.
5. a chorus of thanks/disapproval/protest etc something that a lot of people all say at the same time.
6. in chorus if people say something in chorus, they say the same thing at the same time.

verb
if people chorus something, they say it at the same time.