Definition - What does Deposit mean?
A deposit is an external solid substance that comes into contact with and adheres to the surface of a metal. It may be dirt, rust or other substances generated by or located in the immediate vicinity of the metal.
Corrosionpedia explains Deposit
Deposits are often problematic when adhering to a metal surface. They increase the likelihood of corrosion due to pitting and crevice corrosion on metallic surfaces because they create contact areas where moisture and chemicals can be trapped. Deposits can propagate severe corrosion if not closely monitored.