What do u mean by serum?

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. ... "Serum" is a Latin word that refers to the "whey", the watery liquid that separates from the curds in the process of cheesemaking.
https://nutritions4.com/blossom-nighttime-ageless-serum/