Pillow slips are also known as pillowcases, which are removable covers that protect pillows from dust, sweat, and stains. They are commonly made from cotton, satin, silk, or linen and come in various sizes and colors. Another term for pillow slips is pillow covers, which can be used interchangeably. Some other synonyms for pillow slips include pillow protectors, pillow shams, or simply cases. Pillowcases are essential for maintaining the cleanliness and longevity of pillows, as they can be easily washed and replaced. So, no matter what you call them, pillow slips, pillowcases, or any other synonym, make sure to have a few extras on hand for regular washing and swapping out for a fresh look.