The Transit Visa (Subclass 771) is for persons, who are transiting Australia to another country or passing through Australia to join a ship as crew.
The transit visa allows you to exit the airport area. In general a transit visa is required even if a traveller remains on the same aircraft in the same airport. The visa is valid for up to 72 hours
Note - Certain citizens are eligible to transit without visa arrangements. For more information:
See: Transiting through Australia