(PABX) A telephone exchange operated within an organisation, used for switching calls between iNTernal lines and between iNTernal and PSTN lines. In coNTrast to a PMBX, a PABX can route calls without manual iNTerveNTion, based eNTirely on the number dialed. Not all PABXs can route external calls to iNTernal numbers automatically however. (1998-08-07)