A bed sheet is a rectangular piece of cloth that is used as bedding, either alone or in pairs, and is placed directly below or above the bed occupants. In the many countries where they are used, a top sheet is a flat sheet that lies directly beneath the bed occupants.
What are the purpose of bed sheets?
Fitted sheets are used to cover the mattress, and the elastic band keeps them in place. Their purpose is to protect the mattress and provide you with a smooth, soft surface to lie on.