folk dancer vs dancer

folk dancer and dancer both are nouns.

Word	Noun	Adjective	Verb	Adverb
folk dancer	Yes	No	No	No
dancer	Yes	No	No	No

As nouns, dancer is a hypernym of folk dancer; that is, dancer is a word with a broader meaning than folk dancer:

folk dancer: someone who does folk dances
dancer: a person who participates in a social gathering arranged for dancing (as a ball)

Other hypernyms of folk dancer include social dancer.

folk dancer (noun)	dancer (noun)
someone who does folk dances	a performer who dances professionally
	a person who participates in a social gathering arranged for dancing (as a ball)