Bed sheets are pieces of fabric that are used to cover a mattress and provide a soft and comfortable surface for sleeping. They typically consist of a flat sheet, which covers the top of the mattress, and a fitted sheet, which is placed over the corners of the mattress and tucked under the edges to keep it securely in place. Bed sheets can be made from a variety of materials, such as cotton, linen, or microfiber, and come in a range of sizes and colors to fit different beds and personal preferences.