DEFCON is a "state of alertness", so to speak. It's a general indicator that guides military protocols. It goes from 5 (SSDS, like Call of Duty said. Small localized skirmishes. Normal boring day) to 1 ( Holy frickin' shit, they launched the nukes and some already hit american soil. Nuke'em back and mobilize every last gun toting, uniform wearing personell we have, WW3 started). Worst it ever got was a DEFCON 2 during the cuban missile crisis.