A codicil is a document that amends, rather than replaces, a previously executed will

Will (law)

A will or testament is a legal declaration by which a person, the testator, names one or more persons to manage his/her estate and provides for the transfer of his/her property at death...

. Amendments made by a codicil may add or revoke small provisions (e.g., changing executors), or may completely change the majority, or all, of the gifts under the will. Each codicil must conform to the same legal requirements as the original will, such as the signatures of the testator

Testator

A testator is a person who has written and executed a last will and testament that is in effect at the time of his/her death. It is any "person who makes a will."-Related terms:...

 and, typically, two or three (depending on the jurisdiction) disinterested witnesses.

When confronted with testamentary writings executed after the date of the original will, a probate court may need to decipher whether the document is a codicil or a new will.