Formula racing is any of several forms of open-wheeled single-seater motorsport. 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, Two, Three and 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).