result of the oxidation of iron on steel with moisture or water helping to create a reddish brown color that occurs with iron oxide;
e.g. The rust corroded the pipes, so they had to install a whole new plumbing system.
(noun)
be affected with rust or the reddish- or yellowish-brown flaky coating formed on iron especially when chemically attacked by moist air and composed essentially of hydrated ferric oxide;
e.g. Keep the razor in a dry area so the blades do not rust.