Definition of Serum
The clear yellowish liquid obtained upon separating whole blood into its solid and liquid components after it has been allowed to clot. Also called blood serum. | Blood serum from the tissues of immunized animals, containing antibodies and used to transfer immunity to another individual, called antiserum. | A watery liquid from animal tissue, especially one that moistens the surface of serous membranes or that is exuded by such membranes when they become inflamed, such as in edema or a blister.