https://www.theatlantic.com/politics/archive/2018/04/ranked-choice-voting-maine/557669/

Ranked-choice voting, which cities like San Francisco, Minneapolis, and Portland, Maine, use to elect their mayors, has been likened to an “instant runoff”: Instead of selecting just one candidate, voters rank their choices in order of preference. If no candidate receives a majority of first place votes, the candidate with the fewest votes is eliminated, and whoever their voters chose as their second choice is added to the tally of the remaining contenders. That process continues until there are only two candidates left, and the one with the most votes wins.