Private Branch eXchange
; Private Business eXchange
A telephone exchange that is owned by a private business or a home, as opposed to one owned by a common carrier or by a telephone company. The PBX equipment is typically installed at a business's premises, and connects calls between the telephones installed there. In addition, a limited number of outside lines (called trunk lines) are usually available for making and receiving calls external to the site (i.e. to the public telephone network).