Definition
The total area that a sensor or optical system can observe by moving or steering, including everything it can be aimed at, not just what it sees at any one instant.
Plain English
Everything the sensor could possibly look at if it swiveled to its limits — the full area it can cover, not just what it's pointed at right now.
Context Anchor
Seen in discussions of aircraft sensors, enhanced vision systems, helmet-mounted displays, and other equipment that helps a pilot look outside the aircraft electronically.
Derivation
From the everyday phrase 'field of view' combined with 'regard' (from Old French regarder, meaning 'to look at'). 'Field of view' is the slice you currently see; 'field of regard' is the larger area you could look at by steering the sensor.
Why Pilots Care
Determines how much of the surrounding airspace or ground a sensor or pilot can actually search without repositioning the aircraft.
Analogy
A flashlight beam has a small area it lights up at one moment, but your hand can sweep it across a larger area. The larger area you can sweep across is like the field of regard.
Intuition Check
Do not confuse field of regard with field of view. Field of view is what the system sees right now; field of regard is the full area it can be aimed to cover.
Example Sentence 1
The targeting pod's field of regard covered most of the lower hemisphere, so the crew could slew it to almost any point below the aircraft.
Example Sentence 2
Cockpit pillars reduced the pilot's effective field of regard during the low-level search.