Urns were a type of artefact.
The Urn of Rassilon was one of the artefacts of Rassilon, inside of which was stored the Regeneration Codex. It was kept in Alcove 5-Δ-7-9 of the Omega Vault and was smashed by the Eleven to acquire the device within. (AUDIO: The Eleven)
An urn served as a key for a secret cache in the temple of the Goddess on Gendar. Disguising its true purpose, Virtuoso gave it away to the Vo'lach as a historical relic so that criminals trying to get the cache opened wouldn't strike Gendar itself. This forced Auteur — the Goddess herself — to steal it back with her associates when she needed to retrieve the documents she'd hidden in the cache. (PROSE: The Gendar Conspiracy)
Those selected for execution by Lady Vuyoki's people, including Vuyoki herself, were sealed inside funeral urns covered in elaborate hieroglyphics describing their crimes. Following a celebration, the urns were launched into space on a direct course to the sun known as Marabou. (AUDIO: Time Reef)
On Kastarion 3 the Villengard Ambulance's would compress people into scared remains resembling a urn. (TV: Boom [+]Steven Moffat, Doctor Who series 14 (BBC One and Disney+, 2024).)