Final answer:
A family is a socially recognized group joined by blood, marriage, cohabitation, or adoption, forming an emotional bond and economic unit across cultures.
Step-by-step explanation:
A cross-culturally valid definition of family is a socially recognized group usually joined by blood, marriage, cohabitation, or adoption that forms both an emotional connection and serves as an economic unit of society. This definition encompasses the various forms families can take, including the nuclear family, extended family, and those with fictive kin such as godparents. It recognizes the diversity and adaptability of the family structure, which may not always include co-residence or legal recognition but is characterized by socioemotional ties and often economic cooperation.