A fitted sheet is a type of bed covering designed to fit snugly over a mattress. It has elasticized corners that help it stay in place, preventing it from slipping off during use. Fitted sheets come in various sizes, such as twin, full, queen, and king, to accommodate different mattress dimensions. These sheets are typically made from materials like cotton, polyester, or a blend of fabrics, providing comfort and durability. Fitted sheets are often used as the bottom layer of bedding, serving as a protective barrier between the mattress and the sleeper, while also contributing to the overall aesthetic of the bed.