The defense readiness condition (DEFCON) is an alert state used by the United States Armed Forces.
The DEFCON system was developed by the Joint Chiefs of Staff (JCS) and unified and specified combatant commands. It prescribes five graduated levels of readiness (or states of alert) for the U.S. military. It increases in severity from DEFCON 5 (least severe) to DEFCON 1 (most severe) to match varying military situations.
DEFCONs are a subsystem of a series of Alert Conditions, or LERTCONs, which also include Emergency Conditions (EMERGCONs).(Wikipedia)