bars vs parallel bars

bars and parallel bars both are nouns.

Word	Noun	Adjective	Verb	Adverb
bars	Yes	No	No	No
parallel bars	Yes	No	No	No

As nouns, bars and parallel bars are synonyms defined as:

bars and parallel bars: gymnastic apparatus consisting of two parallel wooden rods supported on uprights

bars (noun)	parallel bars (noun)
gymnastic apparatus consisting of two parallel wooden rods supported on uprights	gymnastic apparatus consisting of two parallel wooden rods supported on uprights