Wikipedia
Yibbum or levirate marriage in Judaism, is one of the most complex types of marriages mandated by Torah law by which, according to the law, the brother of a man who died without children has an obligation to marry the widow. However, if either of the parties refuses to go through with the marriage, both are required to go through a ceremony known as halizah, involving a symbolic act of renunciation of their right to perform this marriage. Jewish law ( halakha) has seen a gradual decline of yibbum in favor of halizah, to the point where in most contemporary Jewish communities, and in Israel by mandate of the Chief Rabbinate, the former is prohibited.
The concept of yibbum is not unique to Judaism. Known as levirate marriage (when the marriage is to the deceased's brother) or widow inheritance (when it is to any surviving male relative), it has been practiced by other societies with a strong clan structure. It is or was known in societies including the Punjabis, Jats, Huns, Mongols, and Tibetans.