PBX stands for private branch exchange. It is basically a business phone system that allows for a network of phones to work together within an organization. PBX systems feature extensions for each phone in the organization, which allow you to have phones hooked up without additional phone lines.
NextPBX's PBX system allows you to set up these extensions, each with the ability to set up voicemail, call forwarding, and utilize features such as the Virtual Personal Assistant and 24/7 Hotline.