Primarily, nap is the raised (fuzzy) surface on certain kinds of cloth, such as velvet or moleskin. Nap can refer additionally to other surfaces that look like the surface of a napped cloth, such as the surface of a felt or beaver hat.
Starting around the 14th century, the word referred originally to the roughness of woven cloth before it was sheared.[1][2] When cloth, especially woollen cloth, is woven, the surface of the cloth is not smooth, and this roughness is the nap. Generally the cloth is then "sheared" to create an even surface, and the nap is thus removed. A person who trimmed the surface of cloth with shears to remove any excess nap was known as a shearman.[3]
Nap typically has a direction in which it feels smoothest. In garments, nap direction is often matched across seams, because cloth will not only feel but look different depending on the direction of the nap. For this reason, sewing patterns frequently show the nap direction, or warn that more fabric will be needed if the fabric has a nap.