The GOP Conference Rules employ a version of ranked-choice voting to find the candidate with majority support in the caucus as a Speaker candidate. If there’s no majority winner when more than two candidates run, the bottom one is eliminated and another vote takes place among the remaining candidates. So supporters for the eliminated candidate get to indicate who their second-choice preference is. Rules reflect view that winner should not be a factional candidate in a plurality-vote system, but someone who can garner a majority of the caucus.

In a small group, this process can be done via a series of separate votes. In RCV, voters rank preferences on a single ballot. hat tip: @MattGlassman312

Update: Unless they change the rules, of course. These are the current rules as of this post.