A nuclear family is defined as:

A nuclear family is characterized as a family structure that typically consists of two parents (a mother and a father) and their biological or adopted children living together in a single household. This configuration emphasizes the relationship between two generations, focusing specifically on the direct lineage of parents and their children, which forms the fundamental unit of a traditional family structure.

The definition captures the essence of a nuclear family, which contrasts with other family forms that might include extended family members, such as grandparents, aunts, uncles, or cousins living in the same household, or scenarios where families are formed through marriage or adoption without a traditional parent combination. Thus, the emphasis on both parents and their children being under one roof aligns precisely with the concept of a nuclear family.