Formula racing is any of several forms of open-wheeled single-seater motorsport road racing. The origin of the term lies in the nomenclature that was adopted by the FIA for all of its post-World War II single-seater regulations, or formulae. The best known of these formulae are Formula One, Formula E, Formula Two, Formula Three, regional Formula Three and Formula Four. Common usage of "formula racing" encompasses other single-seater series, including the GP2 Series, which replaced Formula 3000 (which had itself been the effective replacement for Formula Two).