Optional preferential voting
Optional Preferential Voting (OPV) is a system of vote-casting used in the states of Queensland and New South Wales in the Commonwealth of Australia. Most Australian elections are run under full-preference preferential voting, where all candidates must be numbered in order of the preference of the voter, or the vote will not be counted. Under OPV, voters may choose to mark a preference for one candidate (effectively voting as though it were a first-past-the-post election), all candidates or any number of candidates in between. Although complete numbering is not required under the OPV system (effectively a full-preference vote), single-preference voters are supposed to use a '1' rather than a tick or cross. In practice, ticks or crosses are still considered valid votes as the intention is clear.
In other countries, such as Malta, the Republic of Ireland, and Northern Ireland, full preferences are not required.
This form of voting allows for one single candidate or candidates of similar ideology to be endorsed by a voter rather than directing preferences to all candidates.