Stainless steel is a durable, corrosion-resistant alloy of iron and chromium, often with nickel, that forms a protective oxide layer. It's prized for its strength, hygiene, and long life, leading to wide use in cookware, construction, aerospace, and biomedical applications. There are many grades, such as the common austenitic 304 and martensitic types, each suited for different purposes and environments, with 15 grades being the most used out of over 150 types.