baby grand piano vs parlor grand piano

baby grand piano and parlor grand piano both are nouns.

Word	Noun	Adjective	Verb	Adverb
baby grand piano	Yes	No	No	No
parlor grand piano	Yes	No	No	No

As nouns, baby grand piano and parlor grand piano are synonyms defined as:

Other synonyms of baby grand piano include baby grand, parlor grand, parlour grand, parlour grand piano.

baby grand piano (noun)	parlor grand piano (noun)
a small grand piano	a small grand piano