The term "rigid bus" is used mainly in British English and Australian English and usually only when distinguishing such buses from articulated buses, such as describing a fleet that includes both types. In the case of two-axle buses, which must be single-chassis, rigid vehicles, British English often refers to such vehicles as "two-axle" buses, only using the term "rigid" when referring to vehicles with three or more axles, which can be either rigid or articulated.