Citizens' Ban radio (CB) is, in many countries, a system of short-distance, simplex radio communications between individuals on a selection of 40 channels within the 27 MHz (11 meter) band. The CB radio service should not be confused with FRS, GMRS, MURS, or amateur ("ham") radio. Similar personal radio services exist in other countries, with varying requirements for licensing and differing technical standards. In many countries, CB does not require a license and, unlike amateur radio, it may be used for business as well as personal communications.