beer vs draft beer

beer and draft beer both are nouns.

Word	Noun	Adjective	Verb	Adverb
beer	Yes	No	No	No
draft beer	Yes	No	No	No

As nouns, draft beer is a hyponym of beer; that is, draft beer is a word with a more specific, narrower meaning than beer:

beer: a general name for alcoholic beverages made by fermenting a cereal (or mixture of cereals) flavored with hops
draft beer: beer drawn from a keg

Other hyponyms of beer include draught beer, suds, lager, lager beer, ale.

beer (noun)	draft beer (noun)
a general name for alcoholic beverages made by fermenting a cereal (or mixture of cereals) flavored with hops	beer drawn from a keg