viewers vs audience

viewers and audience both are nouns.

Word	Noun	Adjective	Verb	Adverb
viewers	Yes	No	No	No
audience	Yes	No	No	No

As nouns, audience is a hypernym of viewers; that is, audience is a word with a broader meaning than viewers:

viewers: the audience reached by television
audience: the part of the general public interested in a source of information, entertainment, or a product/service

viewers (noun)	audience (noun)
the audience reached by television	a conference (usually with someone important)
	a gathering of spectators or listeners at a (usually public) performance
	the part of the general public interested in a source of information, entertainment, or a product/service
	an opportunity to state your case and be heard