When we use the term bed linen we are generally referring to the sheets used to cover the mattress so that the sleeper is comfortable and the mattress is protected. If blankets or covers are being used a second sheet needs to be used for comfort between the sleeper and the roughness of the blankets. If a continental quilt is being used the top sheet is usually omitted.

A bed sheet is a rectangular piece of cloth used either singly or in a pair 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). A bottom sheet is laid above the mattress, and may be either a flat sheet or a fitted sheet (a sheet which has been sewn with elastic or a drawstring along the hem of the top, sides and bottom of the sheet to prevent it from slipping off of the mattress). 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.