A leather made from the hide of a calf, used in binding. Calfskin that is used as a writing support is referred to as vellum.
John Carter and Nicolas Barker, ABC for Book Collectors, 8th ed. (New Castle, DE: Oak Knoll Press; London: British Library, 2004)
Raymond Clemens and Timothy Graham, Introduction to Manuscript Studies (Ithaca, NY: Cornell University Press, 2007), 9-13.