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

The correct answer is a will, which is a legally binding document outlining how an individual's assets and property will be distributed upon their death. This document allows the individual—often referred to as the testator—to specify who will inherit their property and under what conditions. A will provides clear instructions and can help to avoid disputes among heirs regarding the distribution of the deceased's estate.

To provide a little more context, an executor is a person or institution appointed by the testator to carry out the terms of the will, ensuring that the deceased's wishes regarding their estate are fulfilled. A testament is another term used in broader contexts related to expressing one's wishes, but it is often synonymous with a will. A codicil is an amendment or addition made to an existing will, allowing for updates without the need to create an entirely new document. Thus, while these terms relate to the management of an estate, a will specifically serves as the overarching document that defines the distribution of property after death.