Serum

noun

1. The clear yellowish liquid obtained upon separating whole blood into its solid and liquid components after it has been allowed to clot.
2. Blood serum from the tissues of immunized animals, containing antibodies and used to transfer immunity to another individual, called antiserum.
3. 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.
4. The watery portion of certain animal fluids like blood, milk, etc; whey.
5. (skincare) An intensive moisturising product to be applied after cleansing but before a general moisturiser.