art gallery vs salon

art gallery and salon both are nouns.

Word	Noun	Adjective	Verb	Adverb
art gallery	Yes	No	No	No
salon	Yes	No	No	No

As nouns, salon is a hyponym of art gallery; that is, salon is a word with a more specific, narrower meaning than art gallery:

art gallery (noun)	salon (noun)
a room or series of rooms where works of art are exhibited	elegant sitting room where guests are received
	gallery where works of art can be displayed
	a shop where hairdressers and beauticians work