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
同义词：floating voter
英汉双解大词典
swing voter(swingvoters)
1.
N-COUNT（可数名词）
A swing voter is a person who is not a firm supporter of any political party, and whose vote in an election is difficult to predict. 游离选民 [美国英语]