Vellum is a thick, fancy type of paper that was traditionally made from animal skin. Today, vellum is much more likely to be made of cotton instead.
If you buy a sheet of vellum from an art supply store, you can rest assured that it's completely vegetarian. Partly because animal skin vellum is so expensive to produce, it's rare these days. Some sacred texts are still printed on the very fine, thin hides of cows, including Torah scrolls. The British Acts of Parliament also continue to be printed on animal vellum. The word vellum shares a root with veal, or "calf meat."