Downtown is a term primarily used in North America by English speakers to refer to a city's sometimes commercial, cultural and often the historical, political and geographic heart. It is often synonymous with its central business district (CBD). Downtowns typically contain a small percentage of a city’s employment. In some metropolitan areas it is marked by a cluster of tall buildings, cultural institutions and the convergence of rail transit and bus lines. In British English, the term "city centre" is most often used instead.