pop group vs ensemble

pop group and ensemble both are nouns.

Word	Noun	Adjective	Verb	Adverb
pop group	Yes	No	No	No
ensemble	Yes	No	No	No

As nouns, ensemble is a hypernym of pop group; that is, ensemble is a word with a broader meaning than pop group:

pop group (noun)	ensemble (noun)
a group that plays pop music	a coordinated outfit (set of clothing)
	the chorus of a ballet company
	a group of musicians playing or singing together
	an assemblage of parts or details (as in a work of art) considered as forming a whole
	a cast other than the principals