A pillowcase is a removable fabric cover that slips over a pillow to keep it clean. Think of it like a jacket for your pillow: it protects the pillow inside from getting dirty from your hair, face, and nighttime drool, and it's much easier to wash than the whole pillow.

Most pillowcases are made from cotton, linen, or other soft fabrics that feel comfortable against your skin. They typically have one open end where you stuff the pillow in, like sliding your hand into a mitten. Some pillowcases have buttons, zippers, or fabric flaps to help keep the pillow from slipping out.

People often choose pillowcases that match their sheets and bedroom colors, but the real purpose is practical: you can pull off a pillowcase and toss it in the washing machine whenever it needs cleaning, which is a lot easier than trying to wash a big, fluffy pillow. Hotels change pillowcases between guests, and at home, most people wash their pillowcases once a week or so to keep them fresh.