Longman Dictionary of Contemporary English
floating voter
noun
EXAMPLES FROM CORPUS
▪ Mr. Ewing I am delighted to learn that you are a floating voter, Mr. Speaker.
Wiktionary
floating voter
n. a person who does not always vote for the same political party, but usually decides on the basis of policies
WordNet
floating voter
n. 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 [syn: swing voter]