Source : Webster's Revised Unabridged Dictionary (1913)

Serum \Se"rum\ (s[=e]"r[u^]m), n. [L., akin to Gr. ???, Skr.
   s[=a]ra curd.] (Physiol.)
   (a) The watery portion of certain animal fluids, as blood,
       milk, etc.
   (b) A thin watery fluid, containing more or less albumin,
       secreted by the serous membranes of the body, such as the
       pericardium and peritoneum.

   {Blood serum}, the pale yellowish fluid which exudes from the
      clot formed in the coagulation of the blood; the liquid
      portion of the blood, after removal of the blood
      corpuscles and the fibrin.

   {Muscle serum}, the thin watery fluid which separates from
      the muscles after coagulation of the muscle plasma; the
      watery portion of the plasma. See {Muscle plasma}, under
      {Plasma}.

   {Serum albumin} (Physiol. Chem.), an albuminous body, closely
      related to egg albumin, present in nearly all serous
      fluids; esp., the albumin of blood serum.

   {Serum globulin} (Physiol. Chem.), paraglobulin.

   {Serum of milk} (Physiol. Chem.), the whey, or fluid portion
      of milk, remaining after removal of the casein and fat.

Source : WordNet®

serum albumin
     n : albumin occurring in blood serum; serves to maintain the
         somatic pressure of the blood