From AMS Glossary
Generic term for any gaseous electrical discharge that produces luminosity.
Thus corona discharge is an example of glow discharge, but point discharge is not. Relatively high electric field strengths are required for glow discharges, for the density of radiatively recombining gas atoms and molecules must be high. While spark discharge and lightning fall under this definition, this term is most commonly applied to the more continuous, quiescent, and less brilliant discharges.