What term describes the children of a parent's siblings of the opposite sex?

The term that describes the children of a parent's siblings of the opposite sex is "cross-cousins." In kinship terminology, cross-cousins refer specifically to the children of a parent's brother and the children of a parent's sister. This relationship is important in many cultures, particularly those that have specific marriage practices or alliances.

For example, if a woman's brother has a daughter and her sister has a son, those children are cross-cousins to each other. This concept often helps define social relationships and obligations within a community. In contrast, first cousins are the children of two siblings who are of the same sex (e.g., a man's children with his sister's children). Half-siblings are those who share one biological parent but not both, while second cousins are the children of first cousins.

Understanding these distinctions helps clarify family relationships and how they might impact social structures, inheritance, and marriage patterns in various societies.