What is RCV?

Ranked Choice Voting refers to voting methods that derive from the Single Transferable Vote (STV). The salient features of the RCV:

• Candidates are ranked in order of preference on the ballot;
• Votes are counted in rounds in which the last-place candidate is eliminated from contention until a candidate is elected;
• When electing more than one candidate, excess votes for newly elected candidates are transferred to candidates that remain in contention; and
• Rankings on the ballot are not counted until all higher rankings have been eliminated, so ranking an additional candidate never hurts the chances an earlier choice is elected.

Why not call it the Single Transferable Vote?

That's not incorrect, but the term "Single Transferable Vote" usually connotes multi-winner elections that achieve proportional representation. In contrast, the term "Ranked Choice Voting" refers to both single-winner (majoritarian) and multi-winner (proportional) applications of STV. RCV does not imply or connote any district magnitude: it is one method for electing any number of seats.

Is it the same thing as Instant Runoff Voting?

Instant Runoff Voting, also known as the Alternative Vote or the Hare method, is a name for Ranked Choice Voting when used to elect a single-member office. That is, it is equivalent to applying the general Single Transferable Vote method to elect a single seat.

Aren't there other voting systems that involve ranking?

Yes, there are a variety of voting systems that ask voters to rank the candidates on the ballot in order of preference, but they are not commonly known as "Ranked Choice Voting." The term Ranked Choice Voting, as defined by jurisdictions that have adopted it, refers exclusively to applications of the Single Transferable Vote as here described.