An independent voter is one who has not declared a preference for a particular political party and votes for either main political party in elections. This is usually predicated on a liking for a particular candidate rather than party.
"Independent" often refers to a politician who does not belong to any political party. In the United States of America, Ross Perot is one of the best-known independent candidates to run for presidential office. In those countries with a two-party system, independents may espouse viewpoints from both parties or may even run on a single issue not favored by either.
Sometimes, even nominal members of political parties are "independents". For instance, Mike Huckabee has been willing to take conservative religious positions that other Republicans have not. He has also taken some positions which could be seen as liberal. For this, many label him an "Independent".