Family is a social definition for a group of people connected by blood with each other, who share the same resources and who live together in the same house.
Generally, the traditional definition of a family includes Father, Mother, Grandparents and Children.
Of course, over time there are several variations and changes that the family definition has undergone. It has adapted to the changing needs of work and social environment. But from an emotional point of view, it remains the same. The group of people who stay with you through your ups and downs, who share the same pains and sorrows, who live in the same living space, who share their resources with each other, who have common life goals, who share the same moral and social values – are your family.
Nuclear family includes two parents [father and mother] and their children living together in the same living space. Till a few decades back this was considered the modern family definition in most parts of the world. This meant that the husband and wife, created their separate family unit after their marriage, separating from their individual parents.
Sometimes due to chance or circumstance, you have the grandparents, cousins of the parents, or cousins of the children staying together in the family unit. This can be called the Extended family structure. This can be a temporary or a permanent arrangement.
Though the definitions of family have changed over time, the emotional need is still the same.