Single Transferable Vote means that voters are able to rank candidates in order of preference, rather than simply pick their most preferred candidate.
In a STV election, candidates must reach a certain number of votes to get elected. This is called a quota. The quota is based on the total number of votes and the number of positions being filled. For example, with 1500 votes cast for a single position, the quota is 750 votes.
The following two examples demonstrate how STV works for electing a Mayor or Council/Board in New Zealand's Local Elections. If you want an even deeper understanding, check out this STV Q&A.
Drag colour candidates here
Rank as many or as few as you'd like to see where your vote would go in the example
Drag candidates here to remove them from your ranking