PABX (Private Automatic Branch Exchange) system is a private telephone network used by organizations to allow internal users to communicate with each other and to share a limited number of external phone lines. It automates call routing, eliminating the need for a human operator, and offers features like call forwarding and voicemail. Modern PABX systems can be digital, analog, or internet-based (IP PABX), with cloud-based options offering increased flexibility and scalability.