Incest (/ˈɪnsɛst/ IN-sest) is human sexual activity between family members or close relatives. This typically includes sexual activity between people in consanguinity (blood relations), and sometimes those related by affinity (marriage or stepfamily), adoption, clan, or lineage.

Whats it called when you marry within your family?

A cousin marriage is a marriage where the spouses are cousins (i.e. people with common grandparents or people who share other fairly recent ancestors). The laws of many jurisdictions set out the degree of consanguinity prohibited among sexual relations and marriage parties.