A dower is the amount of an estate that a widow is entitled to upon the death of her husband, to support herself and her minor children if there be any. Under English and American common law, a widow was entitled to a "life estate" (the use of and the yield from) one-third of the land her deceased husband held at his death. That is why the sale or gift of any of his land prior to his death required the "dower release" (or quitclaim) signature of his spouse on the deed. The term "dower" is related to, but distinct from "Dowry" as explained there.

Source: Black's Law Dictionary, 4th Edition