Source : Webster's Revised Unabridged Dictionary (1913)

Vellum \Vel"lum\, n. [OE. velim, F. v['e]lin, fr. L. vitulinus
   of a calf, fr. vitulus a calf. See {Veal}.]
   A fine kind of parchment, usually made from calfskin, and
   rendered clear and white, -- used as for writing upon, and
   for binding books.

   {Vellum cloth}, a fine kind of cotton fabric, made very
      transparent, and used as a tracing cloth.

Source : WordNet®

vellum
     n 1: a heavy creamy-colored paper resembling parchment
     2: fine parchment prepared from the skin of a young animal e.g.
        a calf or lamb