Source : Webster's Revised Unabridged Dictionary (1913)

Fibrin \Fi"brin\, n. [Cf. F. fibrine. See {Fiber}.] (Physiol.
   Chem.)
   1. A white, albuminous, fibrous substance, formed in the
      coagulation of the blood either by decomposition of
      fibrinogen, or from the union of fibrinogen and
      paraglobulin which exist separately in the blood. It is
      insoluble in water, but is readily digestible in gastric
      and pancreatic juice.

   2. The white, albuminous mass remaining after washing lean
      beef or other meat with water until all coloring matter is
      removed; the fibrous portion of the muscle tissue; flesh
      fibrin.

   3. An albuminous body, resembling animal fibrin in
      composition, found in cereal grains and similar seeds;
      vegetable fibrin.

   {Fibrin factors} (Physiol.), the albuminous bodies,
      paraglobulin and fibrinigen in the blood, which, by the
      action of the fibrin ferment, are changed into fibrin, in
      coagulation.

   {Fibrin ferment} (Physiol. Chem.), a ferment which makes its
      appearance in the blood shortly after it is shed, and is
      supposed to be the active agent in causing coagulation of
      the blood, with formation of fibrin.

Source : WordNet®

fibrin
     n : a white insoluble fibrous protein formed by the action of
         thrombin on fibrinogen when blood clots; it forms a
         network that traps red cells and platelets