snack bar vs milk bar

snack bar and milk bar both are nouns.

Word	Noun	Adjective	Verb	Adverb
snack bar	Yes	No	No	No
milk bar	Yes	No	No	No

As nouns, milk bar is a hyponym of snack bar; that is, milk bar is a word with a more specific, narrower meaning than snack bar:

snack bar: usually inexpensive bar
milk bar: snack bar that sells milk drinks and light refreshments (such as ice cream)

Other hyponyms of snack bar include commissary.

snack bar (noun)	milk bar (noun)
usually inexpensive bar	snack bar that sells milk drinks and light refreshments (such as ice cream)