"If brothers reside together, and one of them dies childless, the dead man's wife shall not marry an outsider. Her husband's brother must come to her, taking her as his wife in a levirate marriage. The firstborn son whom she bears will then perpetuate the name of the dead brother, so that his name will not be obliterated from Israel" -- Deuteronomy 25:5-6.

 

This relationship is called yibum and the one who perpetuates his brother’s memory is called the yavam.  Yavam is an acronym for “yavo ben mimenu” – a child shall come from him.