Anti-corrosion refers to the protection of metal surfaces from corroding in high-risk (corrosive) environments.
When metallic materials are put into corrosive environments, they tend to have chemical reactions with the air and/or water.
The effects of corrosion become evident on the surfaces of these materials. For example, after putting a piece of iron into a corrosive atmosphere for an extended period, it starts rusting due to oxygen interaction with water on the surface of the piece of iron.
Metal equipment lacking any preventive (anti-corrosive) measures may become rusted both inside and out, depending upon atmospheric conditions and how much of that equipment is exposed to the air.
There are a number of methods for preventing corrosion, especially in marine applications. Anti-corrosion measures are of particular importance in environments where high humidity, mist, and salt are factors.