key system - Computer Definition
An inhouse digital telephone system that connects to a number of dedicated system phones. The major difference between a traditional key system and a PBX is that each key system telephone has buttons for outside lines that are dialed directly without having to "dial 9." However, today's key systems are actually hybrids that handle both dialing methods. In addition, they support analog landlines and voice over IP (VoIP) in the same unit.