From SKYbrary Wiki
A magneto is an electrical generator that uses permanent magnets to produce alternating current.
Magnetos that are adapted to produce pulses of high voltage electricity are used in the ignition systems of some gasoline-powered internal combustion engines to provide energy to the spark plugs. Use of the magneto is confined mainly to engines such as lawnmowers and chainsaws where there is no available electrical supply. However, the magneto is also commonly used in aviation piston engines even though an electrical supply is normally available. This is because a magneto ignition system is more reliable than other options such as a battery-coil system.