Parchment is a writing material made from specially prepared untanned skins of animals—primarily sheep, calves and goats. It has been used as a writing medium for more than two millennia. By AD 400 most literature intended for preservation began to be transferred from papyrus to parchment. Vellum is a finer-quality parchment made from the skins of young animals such as lambs and young calves. The generic term animal membrane is sometimes used by libraries and museums that wish to avoid distinguishing between parchment and vellum. Source: Wikipedia (en)