The Collaborative International Dictionary of English v.0.48:

Petrolatum \Pet`ro*la"tum\, n. (Chem. & Pharm.)
   A semisolid unctuous substance, neutral, and without taste or
   odor, derived from petroleum by distilling off the lighter
   portions and purifying the residue. It is a yellowish,
   fatlike mass, transparent in thin layers, and somewhat
   fluorescent. It is used as a bland protective dressing, and
   as a substitute for fatty materials in ointments. --U. S.
   Pharm.
   [1913 Webster]

   Note: Petrolatum is the official name for the purified
         product. Cosmoline and vaseline are commercial
         names for substances essentially the same, but
         differing slightly in appearance and consistency or
         fusibility.
         [1913 Webster]

WordNet (r) 3.0 (2006):

petrolatum
    n 1: a semisolid mixture of hydrocarbons obtained from
         petroleum; used in medicinal ointments and for lubrication
         [syn: petrolatum, petroleum jelly, mineral jelly]