The damage caused by wearing away the surface of a material from contact with another material. When a paint surface is abraded, the paint layer may reveal tiny spots of an underlayer due to the physical disruption of the surface. The paint layer may then appear more matte or thin than it was when first painted. In canvas paintings, abrasion may reveal the pattern of the canvas, since the highest points in the woven fabric will be abraded first. Abrasion is a form of damage that may be caused by aggressive attempts at cleaning a painted surface with strong cleaning agents or solvents or by rough mechanical action.
Source: Looking at Paintings: A Guide to Technical Terms / eds. Tiarna Doherty and Anne T Woollett (Los Angeles: J. Paul Getty Museum, 2009), p. 1.