Vellum is a material made from the skin of calves that was used in period as a writing material. It is the fact that calf skin is used that differentiates it from parchment. It gets its name from the Latin word vitulus, meaning calf.
In order to create vellum the calf skin is cleaned and stretched out on a frame. The skin is alternately wetted, scraped with a knife and then dried until the skin is of the desired thickness. Occasionally pumice and then chalk would be rubbed into the vellum to finish it.