Plain English Meaning

A heavy spinning wheel bolted to the engine. It evens out the engine's running and gives the starter something to grab onto when spinning the engine to life.

Full Definition

A heavy, rotating metal disc attached to the engine's crankshaft that stores rotational energy and smooths out the power pulses produced by the cylinders firing. In the starting system, the flywheel carries a ring gear around its outer edge that the starter motor's pinion gear engages to crank the engine over.

Context Anchor

Seen in engine starting-system discussions, especially when describing how the starter turns the engine before it begins running on its own.