Galvanized iron means the iron is covered by a metal that does not rust, or which only rusts slowly. Iron is usually covered with zinc. The iron cannot rust because the zinc covering protects it.
The zinc resists corrosion even when scraped. After the paint is scratched, metal corrodes. When the zinc has completely corroded, the iron begins to do the same.
There are two ways of galvanising:
Hot dip galvanising: the item is put in a vat of liquid zinc. This gives a longer-lasting, thicker covering. Some people might not appreciate it as much, though, because it does not have a bright, clean surface.
Also possible is electro-galvanizing. This is the process of electroplating zinc onto a surface. Although it is thinner and more sparkly, it does not last as long.