Rust forms as the result of a chemical interaction between a metal and water. The metal in a car, for example, is made partly of steel. The iron in the steel changes over time when it’s exposed to water or constant moisture. You see rust in things that are old, like my car:
There’s a lot of rust around the wheel well. (In this sentence, "rust" is a noun.)
The areas around the wheels have rusted. (In this sentence, "rust" is a verb.)
Some parts of this car have so much rust that they need to be held together with metal straps and coat hangers.
You can prevent rust by keeping your car in a garage.
My car is getting too rusty. (The word "rusty" is an adjective.)
The rear wiper is so rusty, it barely moves any more.