Question

What is serum?

Answer 1

Serum (blood), plasma from which the clotting proteins have been removed.
In blood, the serum is the component that neither contain a blood cell (serum does not contain white or red blood cells) nor a clotting factor; it is the blood plasma not including the fibrinogens.
Blood has plasma where blood cells and clotting factors are suspended,when you remove cells and clotting factors from it you will get clear liquid that is serum.