Private access branch exchange
( rivate utomatic ranch xchange) - Differs from a PBX in that a PBX may require a live operator. Since most PBX systems are now automatic, the term is virtually synonymous with PBX and is not often used.
rivate utomatic ranch xchange. An exchange used for switching calls within an orgnaisation rather than between PSTN subscribers. Most PABX's do have connections to the PSTN for outside calls.