The skin of a animal (sheep, calf or goat) prepared for writing and/or painting. Parchment was used for the production of books in antiquity and the Middle Ages. The finer variety of parchment is called vellum. Web resource here. Video here.
Detail of parchment. Boethius, De institutione arithmetica. Royal Library, The Hague, Netherlands. MS 78 E 59. Ca. 1100 CE.