Plain English Meaning
A careful look-over of the aircraft before flying it, to make sure nothing is broken, missing, or wrong, and that it is safe and ready to go.
Full Definition
A systematic check of an aircraft performed by the pilot before each flight to confirm that the aircraft is airworthy and properly configured for the planned operation. It typically covers a walk-around inspection of the airframe, flight controls, landing gear, propeller, engine compartment, fuel quantity and quality, oil level, lights, antennas, and required documents and equipment, following a checklist specified by the aircraft manufacturer.
Context Anchor
Performed and before every flight, usually with a checklist and a of the aircraft.