A hapū ("subtribe", or "clan") is "the basic political unit within Maori society".
A named division of a Māori iwi (tribe), membership is determined by genealogical descent; a hapū is made up of a number of whānau (extended family) groups. Generally hapū range in size from 150-200 although there is no upper limit. A Maori person can belong or have links to many different hapū. Each hapu had its own chief and normally operated independantly of the tribe(iwi) group. Missionaries such Henry Williams noted that even in times of war against another iwi ,hapu usually operated independently. In the Musket Wars many of the battles were fights between competing hapu rather than iwi. It was not uncommon for 2 hapu from the same iwi to be in conflict.
Hapu frequently were the political unit that sold land to the Europeans. In the 20 years after the Treaty of Waitangi Native Affairs Minister Chris Richmond said that about half of all sales under the Treaty of Waitangi, were by different hapu or comparatively small groups of individuals. He said that all the land sold North of Auckland, some in Hawkes Bay,in the Wairarapa valley, Waikato at Raglan, and by Ngatiawa in Wellington and Taranaki was by hapu or small group.
Before the arrival of Europeans the normal day to day operating group seems to have been the smaller whānau (extended family). By the 1820s Māori had learnt the benefit of working in larger groups especially when it came to trading with ships. The larger hapū could work more effectively to produce surplus flax, potatoes, smoked heads and pigs in exchange for blankets, tobacco, axes and trade muskets. In warfare the hapū was the standard grouping for warriors during the musket war period. Hapū would unite politically under their own chief, to form much larger armies up to several thousand warriors, although it was common for hapū to retain independence within the larger group.
The literal meaning of the word is "pregnant" which is a metaphor for the genealogical connection that unites the members of the hapū. Similarly, the Māori word for land, whenua, can also mean "placenta", metaphorically indicating the connection between the people and the land.