Comment by bwest87

It's where you agree with someone in another state to vote for their preferred candidates and they vote for yours. It generally only makes sense if you are voting for different parties. The reason is because of how America's system for president aggregates by who wins each state, rather than pure popular vote. Many states are so lopsided towards one party that if you are voting with the majority it's kind of a "wasted" vote. So people vote swap to make their vote have more impact.