A clan is a group of people united by kinship. Generally a clan is quite large. Members of a clan generally share a common ancestor three or more generations back (i.e., they share the same great grandparents, great-great grandparents, or an even more distant ancestor). Kin groups who share the same grandparents are generally called extended families, not clans.
A clan is distinguished from other kin-based groups such as tribes and bands by the fact that clans generally exist within a larger society. That society can be a tribe, a chiefdom, or a state, but the clan does not see itself as distinct from the society it lives in. The clans of Scotland and China are two examples.
Most clans are exogamous, meaning that its members cannot marry one another. Some clans have an official leader such as a chieftain, matriarch, or patriarch.
China
The five main Han Chinese Punti clans in Hong Kong are: