What is the X in X-mas?
A type of family in which relatives in addition to parents and children (such as grandparents, aunts, uncles, and cousins) live in a single household. A nuclear family forms the core of an extended family.
an expansion of the nuclear family (parents and dependent children), usually built around a unilineal descent group (i.e., a group in which descent through either the female or the male line is emphasized). The extended family system often, but not exclusively, occurs in regions in which economic conditions make it difficult for the nuclear family to achieve self-sufficiency. Cooperation being necessary, aid is recruited, usually either from the patrilineal kin or the matrilineal kin. In traditional China, for example, the extended family ideally consisted of the nuclear family of the head of the household, his unmarried daughters, his sons and their families, his sons' sons' families and unmarried daughters, and so forth. The extended family may include more distant kin, but the uncles, aunts, or cousins usually belong to the same clan as members of the core lineage.