The life cycle of any release process, be it a completed or a canceled one, ends with the Closure stage. In this stage, the release coordinator associates a closure code for the release. The closure code provides details on whether the release is closed due to cancellation, rejection, completion, or other reasons. This explains to the stakeholders the reason for closing a release request in a nutshell.
The SDAdmin can define release closure codes under Setup >> Customization >> Release Management >> Closure Code.