Final answer:
The custom where a widower marries his deceased wife's sister is called sororate, which helps maintain family connections and care for children.
Step-by-step explanation:
When a widower marries the sister of his deceased wife, this custom is called sororate. This remarriage rule, often observed in various cultures, mandates that a replacement wife, preferably the sister of the deceased, be provided by the wife's lineage. There are practical reasons behind the sororate, such as ensuring that children from the first marriage remain with their father and maintain a connection with their biological mother's family.