sing along

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun colloquial A gathering or event where participants are encouraged to add their voices in song.
• verb idiomatic To sing some music while someone else is singing or playing the same piece of music or while it is being broadcast or performed

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb sing with a choir or an orchestra