noun Blood serum used as a blood product, in the practice of medicine: blood serum from the tissues of immunized animals (human or nonhuman), containing antibodies and used to transfer immunity to another individual (human or nonhuman).
noun 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.
noun The watery portion of certain other animal fluids, such as milk; whey.
noun A skincare product of varying consistencies with a high concentration of one or more active ingredients, for a targeted purpose, such as preventing acne, repairing sun damage, or moisturizing.