The term 'ACTIVATE, AS A SECURITY SYSTEM' can be summarized as the process of turning on a security system to protect a certain area or object. The crossword solution for this term is ARM, which stands for 'Activate, ARM, Monitor'. This is a common acronym used in the security industry to describe the three steps of activating a security system: activating the system, arming it with sensors and alarms, and monitoring it for any suspicious activity.