A more thorough explanation:

Codicil is a legal document that changes or cancels a part of a person's will. It does not replace the original will.

John wrote a will that left all his property to his wife. Later, he changed his mind and wanted to leave some of his property to his children. Instead of writing a new will, he wrote a codicil that added a clause to his original will, leaving some of his property to his children.

Another example could be a person who wants to remove a beneficiary from their will. Instead of writing a new will, they can write a codicil that cancels the part of the will that names the beneficiary.

These examples illustrate how a codicil can be used to change or cancel a part of a will without having to write a completely new will.