<%= link_to "Instant runoff voting", "http://en.wikipedia.org/wiki/Instant_Runoff_Voting" %> is an electoral system in which voters rank candidates in order of preference. In an IRV election, if no candidate receives an overall majority of first preferences the candidates with fewest votes are eliminated one by one, and their votes transferred according to their second and third preferences (and so on), until one candidate achieves a majority.
Instant-runoff voting (IRV) is also known as the Alternative Vote (AV) and by several other names.