Family: 1. A group of individuals related by blood or marriage or by a feeling of closeness. 2. A biological classification of related plants or animals that is a division below the order and above the genus. 3. A group of genes related in structure and in function that descended from an ancestral gene. 4. A group of gene products similarly related in structure and function and of shared genetic descent. 5. Parents and their children. The most fundamental social group in humans.