the.com/nuclear family

means The household unit of two parents and their children, living apart from grandparents, aunts, uncles, and other kin.

from Coined by sociologists in the early-to-mid 20th century, built from Latin 'nucleus' meaning 'kernel' or 'core' — the idea being that this small parent-child unit is the central core around which the larger extended family orbits, the way electrons circle a nucleus. The term caught on as this living arrangement became the idealized norm in mid-20th-century America, standing in contrast to the multigenerational 'extended family' households that came before it.