Defense has several uses in the sphere of military application.

Personal defense implies measures taken by individual soldiers in protecting themselves whether by use of protective materials such as armor, or field construction of trenches or a bunker, or by using weapons that prevent the enemy approaching them to initiate close combat. In close combat where blade weapons are used, defence refers to a specific armed fighting technique.

When applied to military units, defence implies use of defensive tactics that seek to negate enemy offensive tactics.

A defensive military doctrine implies operation of larger military forces from a largely defensive posture, which at the operational warfare scale assumes the form of defenfe in depth, and at strategic scale encompasses a large area of operations such as the Maginot Line by large parts of the French Army before World War II.

In military operations planning, a defensive strategy is the policy of preventing an attack, or minimizing the damage of an attack, by the forces assuming defence in strategic depth for preventing an enemy from conquering territory.

Defense is also a euphemism for war, used by governments to reflect their non-aggressive posture in their region which does not carry the negative connotation of war, such as Ministry or Department of Defense.

Within the scope of a national defense policy, defense is used to include most military issues.

Military science seeks to integrate all the meanings of defence into a coherent whole that seeks to understand and develop applied uses for all of the above meanings within a single national defense management structure.

Although defence of territory, territorial waters and national airspace is one of the functions of the governments of sovereign states in the modern world, Hans-Hermann Hoppe, Murray Rothbard, Morris and Linda Tannehill, and other anarcho-capitalist writers have opined that it could be more efficiently provided by private vendors.