General corrosion, also known as uniform corrosion, is an extremely common form of corrosion. It occurs when a metal surface is exposed to a strongly alkali or acidic material, which eats away at the outermost layer. Normally this damage is purely aesthetic, leaving the underlying structure undamaged.
General corrosion normally affects non-corrosion-resistant materials such as carbon and super duplex stainless steels, which form the instantly recognised bright red iron oxide rust layer throughout.
Because of the increased corrosion resistance of stainless steels, nickel and copper alloys, you are highly unlikely to see general corrosion on them. More likely is localised corrosion in selected areas, where conditions are particularly aggressive or the protective passive film has been damaged.