\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.

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.