Plain English Meaning
The switches in the cockpit that turn the engine's spark-making devices on and off. Each engine has two of these spark-makers, and the switch lets the pilot run one, the other, or both at once.
Full Definition
The cockpit switches that control the aircraft's magnetos, which are engine-driven devices that generate the electrical spark for the spark plugs. Most piston aircraft have two magnetos and a single ignition switch with positions for OFF, L (left magneto only), R (right magneto only), BOTH (normal operation), and START.