2LD: Second-level domain (SLD) is a domain that is directly below a top-level domain (TLD). The top-level domain in this instance is .nz.
Some of these 2LDs are open (available for the public), while others are closer (restricted to certain sectors).
At URL provided, you will find Table 1: 'Domain Names Registered as at 31 December by 2LD (1994-2019)' and 'Table 2: Growth in Domain Names Registered - Calendar Years 1995-2019'. Figure.NZ copied them into an Excel file for processing purposes.