What is an iwi? What is a hāpu?

Iwi

The largest political grouping in pre-European Māori society was the iwi (tribe). This usually consisted of several related hapū (clans or descent groups). The hapū of an iwi might sometimes fight each other, but would unite to defend tribal territory against other tribes.

Iwi-tūturu (the homeland tribe) or tino-iwi (the central tribe) were groups living in a long-held location. They would take their name from a founding ancestor. Iwi-nui or iwi-whānui (the greater tribe) were groups tracing descent from the founding ancestor of the iwi-tūturu. They were often widespread and lived alongside people from other iwi.

Hapū

The most important unit or group in pre-European Māori society was the hapū. Hapū ranged in size from one hundred to several hundred people, and consisted of a number of whānau (extended families). Hapū controlled a defined portion of tribal territory. Ideally, territory had access to sea fisheries, shellfish beds, cultivations, forest resources, lakes, rivers and streams.

source: Te Ara The New Zealand encyclopedia.