What the particular term “anodized” means is that a certain material like the aluminum in cookware has been exposed to an electrolytic procedure, where the natural oxidation has been completely controlled. This entails dipping the aluminum in a bath (chemical) and then applying a current to it. That causes oxide to be generated on the aluminum from the resulting rust. This oxide layer considerably hardens the aluminum and makes it corrosion resistant. Hard anodized is in fact an extension of the procedure using a lower temperature and higher voltage. That leads to more durable and even harder cookware coating.