Defense refers to all the techniques deployed by the ego in conflicts that have the potential to lead to neurosis. Defenses are unconscious because they stem from a conflict between the drive and the ego or between a representation and moral imperatives. The defenses function support and maintain a state of psychic stability by avoiding anxiety and unpleasure. Concept of the defense was broadened somewhat when Freud attributed an important role to the reality principle and to the superego. The function of defense as a mechanism necessary for psychic growth is often overlooked.

Law, and contentions presented by the party against whom a civil action or ciminal prosecution is instituted in order to diminish the plaintiff's cause of action case. The claims of the other party, which asserts reasons why the claims should be disallowed. Defense may involve an absolute denial of the other party's factual allegations or may entail an affirmative defense, which sets forth completely new factual allegations. Pursuant to the rules of federal civil procedure, numerous defenses may be asserted by motion as well as by answer, while other defenses must be pleaded affirmatively.

Defence implies measures taken by individual soldiers in protecting themselves whether by the use of protective materials such as the field construction of a bunker or by using weapons that prevent the enemy approaching them to initiate close combat. Military operations planning, a defensive strategy is the policy of preventing an attack or the minimising the damage of an attack, by the forces assuming defence in strategic depth for preventing an enemy from conquering territory.

Central military organization created by the Congress in 1947, and given its name in 1949. At the end of World War II, the U.S. government decided that a central military organization was needed at the national and the major command levels. In the 1947, Congress created a civilian position with cabinet rank, secretary of defense, a new department, the National Military Establishment, the Air Force and its own department and it made the War Department the Department of the Army and put all three armed services under the new secretary's control.
Department includes the Army, Navy, Air Force, Marine Corps, as well as non-combat agencies such as the National Security Agency and the Defense Intelligence Agency. The Department of Defense has authority over the Coast Guard in peacetime, that agency is under the control of the Department of Homeland Security.