Private Branch Exchange (PBX)

A PBX is a small version of the phone company’s central switching office. All PBX’s are automatic; no operator is needed. A private telephone network is used within an enterprise. Users of the PBX share a certain number of outside lines for making telephone calls external to the PBX.

Broken down, a PBX is;

Private in that the end user owns it.

Branch meaning a small phone company’s central office.

Exchange means the phone company’s central office