A no-fly zone, also known as a no-flight zone (NFZ), or air exclusion zone (AEZ), is a territory or area established by a military power over which certain aircraft are not permitted to fly. Such zones are usually set up in an enemy power's territory during a conflict for humanitarian or military reasons without consent of the enemy state, similar in concept to an aerial demilitarized zone, and usually intend to prohibit the enemy's military aircraft from operating in the region. Military action is employed by the enforcing state and, depending on the terms of the NFZ, may include preemptive attacks to prevent potential violations, reactive force targeted at violating aircraft, or surveillance with no use of force. Air exclusion zones and anti-aircraft defences are sometimes set up in a civilian context, for example to protect sensitive locations, or events such as the 2012 London Olympic Games, against terrorist air attack. A no-fly zone is generally not considered a form of aerial blockade due to its more limited scope compared to an aerial blockade.