Klaf

Klaf or Qelaf (Hebrew: קְלָף) is the designation given a particular piece of skin. The Talmudic definition includes both the form of the skin and the way it is processed, in particular, that it must be tanned. Since the innovative ruling of Rabbeinu Tam (12th century Tosafist) it is primarily used to refer to parchment or vellum. It is one of the materials upon which a sofer writes certain Jewish liturgical and ritual documents.