Avoidance speech in Australian Aboriginal languages is closely tied to elaborate tribal kinship systems in which certain relatives are considered taboo. Avoidance relations differ from tribe to tribe in terms of strictness and to whom they apply. Typically, there is an avoidance relationship between a man and his mother-in-law, usually between a woman and her father-in-law, and sometimes between any person and their same-sex parent-in-law. For some tribes, avoidance relationships are extended to other family members, such as the mother-in-law's brother in Warlpiri or cross-cousins in Dyirbal. All relations are classificatory – more people may fall into the "mother-in-law" category than just a man's wife's mother.