Serum: The clear liquid that can be separated from clotted blood. Serum differs from plasma, the liquid portion of normal unclotted blood containing the red and white cells and platelets. It is the clot that makes the difference between serum and plasma.
Terms in this dictionary with the word "serum" include maternal serum alpha-fetoprotein (MSAFP), serum glutamic oxaloacetic transaminase (SGOT), serum glutamic pyruvic transaminase (SGPT), and serum hepatitis.
The term "serum" also is used to designate any normal or pathological fluid that resembles serum as, for example, the fluid in a blister.
"Serum" is a Latin word that refers to the "whey", the watery liquid that separates from the curds in the process of cheesemaking.