floater

noun

1. 1.Agent noun of float; one who or that which floats.
2. 2.An employee of a company who does not have fixed tasks to do but fills in wherever needed, usually when someone else is away.
3. 3.An unaffiliated player.
4. 4.A voter who shifts from party to party, especially one whose vote can be purchased.
5. 5.A person, such as a delegate to a convention or a member of a legislature, who represents an irregular constituency, such as one formed by a union of the voters of two counties neither of which has a number sufficient to be allowed a (or an extra) representative of its own.