PBX stands for Private Branch Exchange, a telecommunication system designed for businesses and organizations.
A PBX manages internal and external communications by creating an internal telephone network. The purpose of a PBX is reduce the number of inbound phone lines; instead, the phone system is designed around the number of calls that will be made at the same time. Then, the PBX has only the number of phone lines necessary to make all those calls
Traditionally, a PBX was a manual phone system, run by switchboard operators. Today, packet switching technology allows the process of connecting phones within a phone system to be automated.