Definition
Any airspace of the United States, outside an Air Defense Identification Zone (ADIZ), in which the ready identification, location, and control of all aircraft (except for Department of Defense and law enforcement aircraft) is required in the interest of national security.
Plain English
A block of U.S. airspace where every civilian aircraft must be quickly identifiable and trackable for national security reasons, even though it is not part of an ADIZ.
Context Anchor
Seen in airspace, security, and air defense discussions in the Pilot/Controller Glossary and related procedures.
Derivation
From 'defense' (Latin defendere, 'to ward off') and 'area' (a defined region). Together it names a region of airspace set aside specifically for national defense monitoring.
Why Pilots Care
Inadvertent entry without proper clearance can result in military interception or flight deviation.
Intuition Check
A Defense Area is not simply any military area or restricted area. In this FAA meaning, it is a specific kind of national-security airspace outside an Air Defense Identification Zone.
Example Sentence 1
Before the cross-country, the pilot checked the chart to confirm the route did not clip a Defense Area without the required flight plan and transponder code.
Example Sentence 2
ATC confirmed the aircraft's position before authorizing entry into the defense area.