What is the term for a written disposition of property that takes effect upon an individual's death?

The term for a written disposition of property that takes effect upon an individual's death is a "Will." A will is a legal document that outlines how a person's assets and property should be distributed after they pass away. It can also include instructions for the care of any minor children and appoint executors to manage the estate according to the wishes specified in the document.

While trusts, codicils, and deeds are related to estate planning, they serve different purposes. A trust is a legal arrangement where a trustee holds property for the benefit of beneficiaries, and it often takes effect prior to death. A codicil is an amendment or addition to an existing will, thus not a standalone document for property disposition. A deed is a legal document that represents the ownership of property and is used for transferring title, but does not inherently dictate what should happen upon death. Therefore, among all the options, a will is the clear and accurate representation of what constitutes a written disposition of property upon death.