The surface roughening of sheet or strip that develops on subsequent cold deformation if the grain size is too coarse. The appearance is similar to the skin of an orange.
Generally it is the oxide layer spontaneously formed on the surface of a metal or alloy by its reaction with the oxygen in the atmosphere. Specifically in stainless steels it is the protective chromium oxide film that forms on alloys containing more than 10.5% chromium that is impervious to many corroding media. It is why stainless steels are “stainless”.