Simple Definition:

Galvanization is the process of coating a metal object with a protective layer of zinc to prevent it from rusting [the formation of reddish-brown flaky coating on metal].

Example: When a steel fence is galvanized, it is coated with a layer of zinc to protect it from rusting. This helps to extend the lifespan of the fence.

Very Simple Definition:

Galvanization is when a metal object is covered with a special material to stop it from becoming rusty.
Example: When a metal gate is covered with a special coating, like paint, to keep it from rusting, that is called galvanization.