A baking dish is an oven-safe vessel, usually with sides at least two inches deep, used for baking casseroles, gratins, and other dishes that go straight from the oven to the table. It differs from a baking pan mainly by convention: 'dish' usually means a single deep vessel in glass, ceramic, or enameled metal, while 'pan' more often refers to shallower metal bakeware such as sheet pans or cake pans.
Baking dishes are commonly used for lasagna, macaroni and cheese, casseroles, and shepherd's pie. Glass and ceramic versions retain heat well and can usually go from oven to table; metal dishes heat and brown faster.