A mattress cover is a protective layer that fits over a mattress to shield it from dirt, spills, and allergens. It helps extend the life of the mattress by preventing wear and tear, and many covers are designed to be waterproof or hypoallergenic. These covers come in various materials, including cotton, polyester, and memory foam, catering to different comfort preferences. Some mattress covers also feature additional benefits, such as temperature regulation or extra cushioning, making them a popular choice for enhancing sleep quality.