Final answer:
The custom called levirate occurs when a widow marries a brother of her deceased husband.
Step-by-step explanation:
The custom called levirate occurs when a widow marries a brother of her deceased husband. Under the levirate remarriage rule, a widow marries one of her deceased husband's surviving brothers. This practice is common in societies with polygynous families. The purpose of levirate is to ensure the continuity of the family lineage and take care of any young children remaining in the family unit.