Here’s an excerpt from an editorial post by Richard Winger at Ballot Access News:
“Sham candidates” are candidates who have no sincere interest in running for office, but who get on the ballot because one of the more powerful candidates in the same race, or one of the major parties, thinks that the sham candidate’s presence on the ballot will subtract from the total of votes that the other powerful candidate may receive. So, one of the powerful candidates, or parties, initiates the process by which the sham candidate gets on the ballot.
Virtually all attempts at running sham candidates in the general election have failed to achieve their intended purpose. The latest instance of a sham candidate was in the recent special Arizona State Senate election, prompted by a recall petition filed against State Senator Russell Pearce. Backers of Pearce arranged for a sham candidate with a Hispanic surname to appear on the ballot, in hopes that the vote against Pearce would thereby be split. But the sham candidate revealed herself to be a sham candidate by hiding from the media, doing no campaigning, and finally (when the pressure on her was intense) withdrawing from the race.
Read the entire post, including copious examples, here.