A more thorough explanation:

A postnuptial agreement is a legal agreement made between spouses during their marriage to define each spouse's property rights in the event of death or divorce. It is similar to a prenuptial agreement, but it is made after the couple is already married.

For example, a couple may decide to create a postnuptial agreement if one spouse inherits a large sum of money or property during the marriage. The agreement would outline how that inheritance would be divided in the event of a divorce.

It is important to note that a postnuptial agreement is typically created when the couple is not planning to separate or divorce. If the couple is already planning to divorce, a property settlement or marital agreement would be more appropriate.