I could be off the mark here, but I am assuming that it means there is a customary owner and that a buyer may purchase the lease to this land over x amount of years.
I own a block of land in Vanuatu on a 75 year land lease. Instead of paying rates, I pay a small amount each year that goes to a traditional owner of the land. After 75years, I can (or more likely my grandkids) can renew this lease. I can effectively do what I like with the land as if it were freehold. After 75 years, if the traditional owner did not want to renew the lease to me, he/she would have to pay current market value for all "improvements" or structures on the block. As a result, custom leashold is effectively ownership, with a small lease fee that benefits the traditional owners. This is a system that is often exploited, but can also be mutually beneficial.
NZ may be very different tho….