What is galvanization? How does it protect iron from rusting?

Galvanization is the process of coating iron or steel with a thin layer of zinc. It protects iron from rusting in two main ways: 

1. Barrier Protection: The zinc layer acts as a physical barrier, preventing the iron from coming into contact with oxygen and moisture. 
2. Sacrificial Protection: Zinc is more reactive than iron. If the zinc coating is scratched, the zinc will corrode preferentially (sacrifice itself) to protect the underlying iron from rusting, as it will lose electrons more readily than iron.