A PABX, or Private Automatic Branch Exchange, is a telephone system used within an organization to manage incoming and outgoing calls. It connects internal telephones to each other and to external phone lines, allowing for efficient communication without needing a separate line for each phone. PABX systems can be traditional, using physical hardware, or modern, utilizing VoIP (Voice over Internet Protocol) technology. They often include features like call forwarding, voicemail, and conference calling, enhancing the overall communication experience for businesses and their employees.