Plain English Meaning
A careful look-over of the airplane on the ground before flying, where the pilot checks each part of the aircraft against a checklist to make sure nothing is broken, missing, or out of place.
Full Definition
A systematic walk-around examination of the airplane conducted before flight to confirm the aircraft is airworthy and ready for the intended operation. It is performed by visually checking the exterior, control surfaces, landing gear, powerplant, fuel and oil quantities, and other items specified in the airplane's approved checklist or pilot's operating handbook.