Corrosion is non-uniform if the time average of the corrosion current through a unit area depends on its position on the surface. Non-uniform corrosion can be due to inhomogeneities of structure or of composition of the corroding material, or to inhomogeneities of the environment. Special cases of non-uniform corrosion such as pitting or intergranular corrosion are sometimes called localized corrosion.
PAC, 1989, 61, 19. 'Electrochemical corrosion nomenclature (Recommendations 1988)' on page 21 (https://doi.org/10.1351/pac198961010019)