Plain English Meaning

Blowing warm air on the inside of the windshield to clear the fog so the pilot can see out.

Full Definition

The process of clearing condensation, mist, or frost from the inside surface of an aircraft windshield by directing warm, dry air across the glass. In small airplanes equipped with a combustion heater, defogging is typically accomplished by routing heated air through dedicated windshield outlets at the base of the windscreen.

Context Anchor

Seen in aircraft heating and ventilation discussions, especially when a cabin heater also provides air to clear the windshield.