Surface application is a process in which a coating is applied to a surface. The most common type of surface application is painting, but other coatings such as varnish, lacquer, and enamel can also be used. The purpose of surface application is to protect the surface from damage, enhance its appearance, and/or provide a decorative finish. COAT is a four-letter word that is often used to refer to a layer of paint or other material applied to a surface.