A PBX is a Private Branch eXchange.
Did you ever dial 9 on your business phone to get an outside line?
That’s a PBX!
It’s a device – typically physical hardware like a PC – that hooks up to both phone lines from the phone company and the phone lines inside your office. But with modern phone equipment dialing 9 is largely done away with – the phone can be programmed/configured better than that. And with Voice over internet Protocol (VoiP), your Ethernet data lines can now do the work that only voice telco lines used to do, with much less wiring. Today, if you opt for a virtual machine, then with the right telephone company, your PBX services can live almost entirely in software!