The voting system used in the ACT in which an elector shows by numbers his/her preference for individual candidates but does not need to show a preference for all candidates listed for the vote to be formal.

The process of voting in which electors have a choice of whether to mark a second or further preferences for other candidates, as well as their first preference (see also Preferential voting).

A modification of the preferential voting system (which normally requires the sequential numbering of each candidate to cast a valid vote) that allows the elector to elect not to provide a number for one or more candidates. In this system of voting, a vote may "expire" and not be counted in the final tally if all of the voter's number candidates are eliminated.

A form of preferential voting that does not require electors to mark preferences for all candidates listed on the ballot-paper. This method of voting could be seen to be disadvantageous to some allied groups that benefit from the flow on of one another's preferences. Further explanation of Optional Preferential Voting is available in the animated presentation "How Your Vote Counts".

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 strict rules of preferential voting, where all candidates must be numbered in order of the preference of the voter, or the vote will not be counted. Although complete numbering is not required under the OPV system, a single-preference vote must still use a '1' and not a tick or cross in order for the cast vote to be considered valid.