In military terminology, a battalion consists of two to six companies typically commanded by a lieutenant colonel. The nomenclature varies by nationality and by branch of arms, e.g. some nations will organize their infantry into battalions but call similarly sized units of cavalry, reconnaisance, or tanks a squadron instead. There may even be subtle distinctions within a nation's branches of arms, such a distinction between a tank battalion and an armored squadron, depending on how the unit's operational role is perceived to fit into the army's historical organization.
A battalion is potentially the smallest independent military unit (i.e. not attached to a higher command) but is usually part of a regiment or in the United States Army a brigade. Battalions are ordinarily homogeneous with respect to type, i.e. an infantry battalion or a tank battalion, though there are occasional exceptions.