Talaq al bai'in refers to an irrevocable divorce. It is a type of divorce in Islamic law that terminates a marriage and cannot be undone. The term "bai'in" means "clear" or "explicit," indicating that this type of divorce is final and cannot be reversed. In this type of divorce, the husband pronounces the divorce in a clear and unambiguous manner, and the wife is immediately free to marry someone else if she chooses to do so.