bars vs uneven bars

bars and uneven bars both are nouns.

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

As nouns, uneven bars is a hyponym of bars; that is, uneven bars is a word with a more specific, narrower meaning than bars:

bars: gymnastic apparatus consisting of two parallel wooden rods supported on uprights
uneven bars: a pair of parallel bars set at different heights; used in women's gymnastics

Other hyponyms of bars include uneven parallel bars.

bars (noun)	uneven bars (noun)
gymnastic apparatus consisting of two parallel wooden rods supported on uprights	a pair of parallel bars set at different heights; used in women's gymnastics