The term 'ACTIVATING, AS A SECURITY SYSTEM' can be summarized as the process of ARMING a security system. This is the process of enabling a security system to detect and respond to potential threats. It involves setting up sensors, alarms, and other components that will alert the user when an intruder is detected. The term ARMING (6 letters) is used to describe this process, which is typically done by entering a code or pressing a button.