1. A transient or continuous conduction of electricity through a gas by the formation and movement of electrons and ions in an applied electric field.
2. The flow of electricity through a gas, resulting in the emission of radiation that is characteristic of the gas and of the intensity of the current.
3. The removal of a charge from a battery, capacitor, or other electric-energy storage device.
4. The passage of electricity through a gas, usually accompanied by a glow, arc, spark, or corona.