3-58. Seizing or retaining terrain that provides advantages to friendly force maneuver allows commanders to gain and maintain positions of relative advantage. For military purposes, terrain includes physical (geographic) and non-physical (virtual and cognitive) components. Commanders and staffs include the cognitive and virtual considerations of an operational environment when describing terrain. Terrain that is of importance to commanders is described as key or decisive terrain. Key terrain is an identifiable characteristic whose seizure or retention affords a marked advantage to either combatant. Decisive terrain is key terrain whose seizure and retention is mandatory for successful mission accomplishment. If decisive terrain is present, commanders designate it to communicate its importance in the commander’s concept of operations, first to the echelon staff and later to subordinate commanders.