The term PART OF A SKIN CARE ROUTINE can be solved by the five-letter word SERUM. Serums are a type of skincare product that are typically applied after cleansing and toning, but before moisturizing. They are usually made up of smaller molecules than moisturizers, allowing them to penetrate deeper into the skin and deliver active ingredients more effectively. Serums are often used to target specific skin concerns such as wrinkles, dark spots, and acne.