Approval Voting allows each voter to Approve or Disapprove of each candidate. The candidate with the most Approve votes wins. In other words, there is a Yes-or-No vote on each candidate, and the winner is the candidate with the highest approval rating.
In this system, voters indicate all candidates of whom they approve, so the outcome better reflects the will of the voters. This eliminates the possibility of a "spoiler effect", thus leveling the field for third-party candidates. It also leads to the election of candidates with central positions that all sides approve of, reducing partisanship.
Aproval Voting is a major improvement over both our current "First Past the Post" system and "Instant-Runoff Voting". It is the simplest form of Range Voting, and the best for general elections.