A term used by painting conservators to describe the loss of paint caused by friction during improper varnish removal. Abrasions occur both on canvas art and paintings on other materials such as wood or metal board.
Another common cause of abrasion is simply friction of any kind. Without due care and attention, a painting can rub against other objects during transit between one location and another. It goes some way to explaining why condition reports before and after a relocation are so commonplace in the world of art. House proud private owners may clean or dust off the art frequently, and abrasion happens to any painting with age where the frame touches the painted surface.
Finally, Scratches can be classed as abrasions, often resulting in a loss on the surface, extending to the paint and ground layers.
In the past art restorers would work directly on the canvas in the damaged areas. However, it is now more common not to blend the brushwork from the original artist with that of the restorers. Hence the restoration expert seals off the area with varnish and works on top the varnished layer. It is a reversible restoration technique in the sense that future restorers can remove previous restoration work with the varnish.