Lightning can be defined as a transient, high current electric discharge whose path length is generally measured in kilometers. Lightning occurs when some region of the atmosphere attains an electric charge sufficiently large that the electric fields associated with the charge cause electrical breakdown of the air. However lighting has been reported in snowstorms, sandstorms, in clouds over erupting volcanoes, and been reported to occur in the clear air.

Such lightning can take place entirely within a cloud (intra cloud), between two clouds, between cloud and the earth, or between a cloud and the surrounding air.