A bed sheet is a rectangular cloth used to cover a mattress and those sleeping upon it. They are the sheets which one typically lies between. In many places a second flat bed sheet is laid on top of the sheet covering the mattress. When a second sheet is used, the top one is known as the top sheet and the sheet covering the mattress is known as the bottom sheet or “coupie sheet” in some European countries. If the bottom sheet is presewn to fit snugly over the mattress, it is known as a fitted sheet. Blankets, quilts / duvets / comforters, and other bed covers are placed on top of the top sheet.