NZBDM is an abbreviation for the official record source displayed by Template:nzbdm: New Zealand Births, Deaths & Marriages Online: https://bdmhistoricalrecords.dia.govt.nz/search
Searching the indexes is free for events that happened 80 or 100 years ago or varying dates depending on the type of event. Precise dates can be found, sometimes earlier than the registration year, by progressive narrowing of the search date range. More detail, however, requires payment.
Switching between birth, death, and marriage indexes can be done with a single click on each page.