A bedskirt or dust ruffle is a decorative covering that is placed under a mattress and over a box spring. The skirt hangs to the floor to cover and hide whatever may be under the bed. These box spring covers add a fashionable, finished look to your bedroom and come in a variety of fabrics and styles including tailored, pleated, tiered or ruffled. Although a bedskirt is the final touch to any bedding set, it is usually the one piece you lay and leave year-round. So making sure you place the right one is an absolute must.