Rank Choice Voting (RCV) is a way of voting that permits voters to rank their choice of candidate in order of preference. RCV only applies when more than two candidates are running for the same office. When only two candidates are running for the same office, the winner will receive a majority of the votes cast, by definition. RCV ensures that when more than two candidates are running, the candidate who wins the election will be a preference of a majority of the voters.
So instead of voting for just one candidate like we do now, in an election where RCV is used, voters will rank the candidates: 1st choice, second choice, third choice, and so on. Instead of just voting for one candidate, voters rank-order their preferences of candidates, relative to each other. Voters are not required to rank all candidates. They may rank order only those candidates they would find acceptable.