Cloth cover for a small pillow.
If you've ever slept on a bare, white pillow, you may have noticed it gradually turns yellow until it becomes dirty, filthy, and unsightly! A pillow cover, or pillowcase, helps protect the pillow underneath by covering it and catching the hair, sweat, and drool that the poor pillow would otherwise have to face. They are usually made out of cloth, silk, or synthetic materials. Pillowcases come in a "bag" form, which allows them to be removed from their pillow and washed separately, which can also give the sleeper a sense of cleanliness, being able to sleep on a freshly washed pillowcase instead of a pillow that hasn't seen soap in a decade.
Found in home furniture stores, bedrooms, and hotel rooms.