A three piece comforter set typically includes a comforter, a bedskirt, and one or two pillow shams. The comforter is the main component of the set and is usually reversible, meaning it can be used with either side facing up. The bedskirt goes around the perimeter of the mattress and helps to create a finished look. Pillow shams are decorative pillows that coordinate with the comforter and complete the overall aesthetic of the bed.