A bed sheet is a rectangular piece of cloth used as bedding, which is larger in length and width than a mattress, and which is placed immediately above a mattress or bed, but below blankets and other bedding (such as comforters and bedspreads or sheets). A bottom sheet is laid above the mattress, and may be either a flat or fitted sheet. A top sheet, in the many countries where they are used, is a flat sheet, which is placed above a bottom sheet and below other bedding