The Alternative vote is a different approach to voting, and uses a preferential system, rather than proportional representation.
Voters rank candidates in order of preference, rather than just voting for one individual.
So each voter has one vote, but rather than marking an x by their chosen candidate’s name, they number the candidates in order of preference, until they no longer have a preference. If a candidate gains more than half the vote as first preference, they are elected outright.
However if not, the candidate who lost (the one with the least first preferences) is eliminated and their votes move to the second preference marked on the ballot papers. This process will continue until one candidate has half the votes and is elected.
Check out this video for more examples of the Alternative Vote explained.