Galvanization is the process of electro-plating steel or iron with zinc. This is done to reduce corrosion (specifically rusting) of the steel or iron item. The zinc coating prevents oxidation of the protected metal by forming a barrier. Zinc oxide in contrast to iron oxide is a fine white dust which does not cause a break down of the zinc's surface integrity as it is formed. Indeed the zinc oxide if undisturbed can act as a barrier to further oxidation in a similar way to the protection afforded to aluminium and stainless steels.
Galvanic or sacrificial anode protection uses ingots of zinc electrically bonded to the metal it is to protect where the metals will be subject to an electrolytic solution. In such a solution the zinc is absobed into the electrolyte in preference to the metal that it protects.
Obviously in some environments both mechanisms can be at work. For example the traditional measure of a coating's effectiveness is resistance to a salt spray.