What term refers to two kinship groups that together form a tribe or society?

The term that refers to two kinship groups that together form a tribe or society is "Moieties." In anthropological terms, moieties are each of the two divisions within a society, often representing a means of organizing social structures and obligations. These divisions can help in establishing relationships, alliances, and responsibilities among individuals belonging to the respective kinship groups.

Moities are significant in many cultures, particularly when it comes to the distribution of resources, social roles, and the structuring of marriages and inheritance practices. Understanding the concept of moieties allows anthropologists to analyze how societies organize themselves and the implications such structures have on social interactions and cultural practices.

The other options relate to different aspects of kinship or family structure but do not fit the definition provided in the question. For example, a phratry is a larger group made up of several clans and not strictly two groups. Matrilocal refers to a residence pattern following the wife’s family, while a nuclear family describes a family unit consisting of parents and their immediate children, which does not encapsulate the idea of two distinct kinship groups forming a larger societal structure.