Defense

Defense in the military is a way of fighting which aims to repel the attack of a more significant number or greater power of the enemy's forces, inflict maximum losses on him, hold important areas (objects) of the area and in this way create favorable conditions for the transition to the offensive.
The defense can be prepared in advance or organized during the battle, in the conditions of a collision with the enemy or another encounter with him.
In defense, each soldier, using his weapons, fortifications, and favorable terrain conditions, can destroy a large number of the enemy's manpower and successfully fight against his advancing tanks and other armored vehicles.
A platoon (department, tank) has no right to leave a defensive stronghold (position) and leave without an order from the command.[Радянська військова енциклопедія]
Defense is an effort to protect the citizens of a state from man-made and natural disasters. It uses the principles of emergency operations: prevention, mitigation, preparation, response, or emergency evacuation and recovery. Programs of this sort were initially discussed at least as early as the 1920s and were implemented in some countries during the 1930s as the threat of war, and aerial bombardment grew. Civil-defense structures became widespread after authorities recognized the threats posed by nuclear weapons.

Sources:

Lord J. (1978). Enterprise vs Bureaucracy. Oxford: Pergamon Press. (p. 204)