Trans-Tasman Travel Arrangement
The Trans-Tasman Travel Arrangement (TTTA) is an arrangement between Australia and New Zealand which allows for the free movement of citizens of one of these countries to the other. The arrangement came into effect in 1973, and allows citizens of each country to reside and work in the other country indefinitely, with some restrictions.
Source: Wikipedia — Trans-Tasman Travel Arrangement (CC BY-SA 4.0)