A term used to describe
negative campaigning in
politics, where the
candidates would accuse each other of
horrible and
nefarious acts which are probably not true, in an attempt to
discredit the other
candidate and win the
election.
As far as I know, American mudslinging in national politics began with the 1828 presidential campaign of Andrew Jackson (aka Old Hickory) against the Whig Party. Apparently the Second Bank of the United States didn't like him and threw all their resources against him, and the resulting battle composed of several accusations and slander focused on the two candidates. Jackson's wife died after a sickness she got after being accused of being unfaithful. Jackson got very pissed and retaliated. He won.
Since then, mudslinging has become a part of political campaign. An interesting note is that it always targets the more radical of the political targets (e.g. Alan Keyes) and make it a generalization. Blatantly wrong, but then again, politicians would do anything to win an election.