A purple state is a state with a vote which is typically closely divided between Democratic and Republican candidates at election time. As a result, such states can become important areas for electoral contests, with candidates fighting to get the majority of the vote so that they can win. The “purple” in the name is a reference to the fact that as election results come in, states are typically colored red or blue to indicate a win by a Republican or Democratic candidate, and purple is a blend of these two colors.
You may also hear a purple state called a swing state, because the vote can swing either way, or as a battleground state, in a reference to the fact that candidates sink serious resources into purple states, often long before the election. The outcome of the vote in such states can become crucial, with most candidates relying on a base of states which vote in a dependable way, and focusing on the purple states to fight for the win.
Swing states have become an issue thanks to the electoral college system in the United States, which awards the Presidency on the basis of a winner-take-all system in individual states. For example, if a candidate wins 40% of the vote in Idaho while two other candidates split the remaining 60%, he or she takes all of the electoral votes for that state. Thanks to the electoral college, candidates may win the election without winning the popular vote, and they have no real incentive to increase the number of voters in any given state beyond the majority needed to win.
At issue in a purple state is the fact that the citizens have very mixed values. Often, a county by county analysis of a purple state reveals pockets of political sentiment, with some counties being decidedly Republican or Democratic, and in a sense canceling each other out in a vote. The goal of a politician when dealing with a purple state is to draw people who are undecided about the candidate they want to support, in the hopes of getting just enough of a majority to take the state.
Various states have fluxed in and out of purple state status. As a general rule, people look at the history of elections in an individual state to determine whether or not it is a swing state. Florida is perhaps one of the most notorious swing states of the 21st century, thanks to the heavy influence Florida's closely split vote had on the outcome of the 2000 Presidential election, but other swing states include Ohio, New Mexico, New Hampshire, Nevada, Arkansas, Virginia, and Missouri, among others.
Typically, a purple state will see a lot of campaign advertising in advance of the election, and politicians will make an effort to visit early and often to connect with voters. This can leave residents of so-called “safe states” feeling a bit left-out, and irritated by the presumption of candidates who assume that these states will go to them.