A concession (discounted fare) can be applied to a Snapper card.
Concessions are reduced fares offered to certain groups of public transport users subject to certain eligibility criteria. Greater Wellington Regional Council sets the standard Metlink fares and concessions, such as the child concession. There are a number of other targeted concessions (IHC, Blind and Cable Car tertiary concessions) offered by operators and other organisations.
You can only have one concession on your Snapper card at any given time, and need to register the card you want to apply a concession too.