serum

  1. Watery proteinaceous portion of the blood that remains after clotting. Synonym: blood serum
  2. Clear watery fluid especially that moistening the surface of serous membranes or that exuded through inflammation of any of these membranes.
Source:
PAC, 2004, 76, 1033 (Glossary of terms used in toxicokinetics (IUPAC Recommendations 2003)) on page 1070