PBX

PBX stands for private branch exchange, a telephone switching system that serves a single organization such as a business or hotel.

A PBX routes calls between internal extensions and connects them to outside lines, allowing many employees to share a limited number of external phone lines.

Before digital systems, these were physical switchboards requiring operators; modern PBX systems are often software-based and may route calls over the internet.

The office PBX went down, so nobody could make calls.