A more thorough explanation:

Definition: A type of will where two or more people, usually a married couple, make separate but identical wills that leave their property to each other. It is also possible for them to make a single mutual will. This type of will is also known as a reciprocal will, counter will, double will, or joint and mutual will.

Example: John and Jane are a married couple. They both make separate wills that leave all their property to each other. They both name their children as the alternate beneficiaries if their spouse dies before them. These wills are mutual testaments.

Explanation: In this example, John and Jane have made separate but identical wills that leave their property to each other. This means that if one of them dies, the other will inherit everything. They have also named their children as alternate beneficiaries if their spouse dies before them. This type of will is called a mutual testament because it is made by two or more people who establish identical or similar testamentary provisions disposing of their estates in favor of each other.