What is a nap in sewing?

A nap in sewing refers to the direction of the fibers of fabric, which can affect the appearance and texture of the finished product. Nap is more commonly found in fabrics like velvet, corduroy, and some types of upholstery fabric. The direction of the nap can cause the surface of the fabric to appear either lighter or darker, or to have a different texture depending on the angle at which it is viewed. When sewing with a fabric that has nap, it is important to cut all pieces in the same direction and to align the nap correctly to ensure a uniform appearance in the finished project.