light·ning
Pronunciation:'lIt-ni[ng]→ n.
the occurrence of a natural electrical discharge of very short duration and high voltage between a cloud and the ground or within a cloud, accompanied by a bright flash and typically also thunder: a tremendous flash of lightning.

 
   
 
The electric current passing through the discharge channels rapidly heats and expands the air into plasma producing acoustic shock waves (thunder) in the atmosphere. The discharge may take place between one part of a cloud and another part (intracloud), between one cloud and another (intercloud), between a cloud and the earth, or earth and cloud.
   
 
Lightning may appear as a jagged streak (forked lightning), as a vast flash in the sky (sheet lightning), or, rarely, as a brilliant ball (ball lightning). Illumination from lightning flashes occurring near the horizon, often with clear skies and the accompanying thunder too distant to be audible, is referred to as heat lightning. There are numerous theories on why charges accumulate in the atmosphere.
   
 
It is thought that temperature and water vapor pressure in thunderstorm clouds are associated with the positive and negative ions that cause lightning. Long-lasting lightning flashes with lower current are more damaging to nature and humans than shorter flashes with higher currents. Benjamin Franklin, in his kite experiment (1752), proved that lightning and electricity are identical