tavern vs beer garden

tavern and beer garden both are nouns.

Word	Noun	Adjective	Verb	Adverb
tavern	Yes	No	No	No
beer garden	Yes	No	No	No

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

tavern: a building with a bar that is licensed to sell alcoholic drinks
beer garden: tavern with an outdoor area (usually resembling a garden) where beer and other alcoholic drinks are served

Other hyponyms of tavern include bucket shop, gin mill, pothouse, pub, public house, saloon, taphouse, rathskeller, shebeen.

tavern (noun)	beer garden (noun)
a building with a bar that is licensed to sell alcoholic drinks	tavern with an outdoor area (usually resembling a garden) where beer and other alcoholic drinks are served