This indicates the expected electrical polarity -- active-high versus active-low -- wired into a discrete external alarm input pin, and per the description is meaningless (always false) for the device's own internal alarms. Because external contacts like door sensors or generator-fail contacts can be wired either normally-open or normally-closed depending on site cabling, this tells the admin how to correctly interpret a true reading on that specific input without guessing at wiring conventions. For example, a site using a normally-closed door contact wired to alarm input 2 would set this true so the device knows an open circuit, not a closed one, means the door is actually open.