Iroquois kinship (also known as Bifurcate merging) is a kinship system used to define family. Identified by Louis Henry Morgan in his 1871 work Systems of Consanguinity and Affinity of the Human Family, the Iroquois system is one of the six major kinship systems (Eskimo, Hawaiian, Iroquois, Crow, Omaha, and Sudanese).
The system has both classificatory and descriptive terms; in addition to gender and generation, also distinguishes between parental siblings of opposite sexes. Parental siblings of the same sex are considered blood relatives. However, parental siblings of differing sex are labelled as "Aunt" or "Uncle as the situation necessitates. Thus, one's mother's sister is also called mother, and one's father's brother is also called father; however, one's mother's brother is called father-in-law, and one's father's sister is called mother-in-law.
Children of the parental generation are considered siblings (parallel cousins). The children of an Aunt or an Uncle are not siblings, they are instead cousins (cross counsins specifically).