voter vs swing voter

voter and swing voter both are nouns.

Word	Noun	Adjective	Verb	Adverb
voter	Yes	No	No	No
swing voter	Yes	No	No	No

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

voter: a citizen who has a legal right to vote
swing voter: a voter who has no allegiance to any political party and whose unpredictable decisions can swing the outcome of an election one way or the other

Other hyponyms of voter include constituent, crossover, crossover voter, floater, floating voter.

voter (noun)	swing voter (noun)
a citizen who has a legal right to vote	a voter who has no allegiance to any political party and whose unpredictable decisions can swing the outcome of an election one way or the other