Definition - What does Weathering mean?
Weathering is the physically noticeable changes in a paint or coating layer due to exposure to external factors.
Corrosionpedia explains Weathering
Weathering is an indicator of corrosion in metal surfaces. It is often identifiable by changes in colour, texture, strength and other physical properties. The term "weathering" may also refer to a type of high-strength, low-alloy steel (made in the 1930s), which is highly resistant to corrosion.