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. Typically made from materials like cotton, polyester, or a blend, fitted sheets provide a smooth surface for sleeping. They are often used in conjunction with a flat sheet and other bedding items, such as comforters or duvets, to create a complete bedding ensemble.