What is the term for placing cremated remains in an urn or grave?

Inurnment is the correct term for the act of placing cremated remains into an urn or a grave. It specifically refers to the final step of the cremation process where the ashes are secured in an urn, which can then be kept in a designated location, such as a home, a columbarium, or buried in a grave. This term is derived from the word "urn," which delineates the specific container used for the ashes.

Other terms in the question relate to different aspects of handling remains after death. Interment generally refers to the act of placing a body in a grave, typically associated with traditional burial practices, whereas inhumation specifically describes the burial of a body in the ground. Disposition is a broader term that encompasses all forms of handling remains after death, including burial, cremation, and other methods. Therefore, inurnment is the precise term that captures the action of placing cremated remains into an urn.