Definition
Wedge-shaped blocks placed snugly against the front and/or back of an airplane's tires to prevent the airplane from rolling while parked or during ground operations such as hand propping.
Plain English
Small wedges put against the wheels so the airplane cannot roll forward or backward when it is parked or when the engine is being started by hand.
Context Anchor
Seen during parking, preflight, engine starting, and especially hand propping procedures.
Derivation
Chock' is an old English/nautical word for a wedge or block used to hold something steady, originally used to keep barrels and small boats from rolling. The aviation use carries the same idea over to airplane wheels.
Why Pilots Care
Prevents the aircraft from rolling unexpectedly, which is critical during hand propping to avoid injury or damage.
Analogy
Wheel chocks work like a strong doorstop, but for airplane tires.
Intuition Check
Wheel chocks are not the aircraft’s brakes. They are separate blocks placed outside the airplane against the tires to help hold it still.
Example Sentence 1
Before hand propping the airplane, the pilot set the parking brake and placed wheel chocks in front of and behind the main tires.
Example Sentence 2
After tying down the airplane, the student added wheel chocks to keep it from moving in the wind.