Definition
A cylindrical component that moves up and down inside an engine cylinder, transmitting the force of expanding combustion gases through a connecting rod to the crankshaft. The piston seals the combustion chamber with a set of rings and is one of the primary moving parts of a reciprocating engine.
Plain English
A solid metal plug that slides up and down inside a tube-shaped cylinder. When fuel burns above it, the push drives it down, and that motion is what turns the engine.
Context Anchor
You will see this term in aircraft engine descriptions, maintenance discussions, compression checks, and explanations of how engine power is produced.
Derivation
From the French piston, originally meaning a pestle -- the rod you push down into a mortar to grind something. The image is the same: a snug-fitting plug pushed up and down inside a cylinder.
Why Pilots Care
Proper piston function is essential for engine power and reliability; worn pistons can lead to loss of compression and engine failure.
Analogy
Think of a bicycle pump. The handle you push down is acting like a piston -- a snug plug sliding inside a tube, moving air with each stroke. In an engine, the burning fuel pushes the piston instead of your hand.
Grounding Statement
Picture one cylinder in the engine: the piston slides inward and outward in that cylinder, and each strong push helps keep the engine turning.
Intuition Check
Do not think of the piston as the part that burns the fuel or as a wheel that spins. The piston slides back and forth; other engine parts turn that back-and-forth motion into rotation.
Example Sentence 1
During the power stroke, expanding gases force the piston down, turning the crankshaft.
Example Sentence 2
The mechanic inspected the piston rings for signs of wear during the engine overhaul.