Lightning is an electrical discharge in the atmosphere between clouds and ground. It's basicly a path for the current to flow down to ground and it happens in microseconds with enormous rise in heat, pressure and energy at strike point.
Lightning is the major threat for regions like Africa, South Asia, North America, Latin America and Australia
Lightning clouds are usually vertically developed (cumulative) type and large enough to contain different charge groups inside at different heights. CumuloNimbus (Cb) clouds are the ones where lightning is mostly observed. Bottom layer of this cloud is at around 500 meters above the ground and top layer may rise up to 8000 meters in the atmosphere. Cb clouds have different charge groups inside and bottom layer is usually negatively(-) charged where the top layer has positive(+) charges mostly.
Negatively charged bottom layer of Cb attracts the opposite charges from the structures on the ground, so the area under the cloud gets positively charged and all negative charges leave the area.
As the storm grows up, negative charges start moving downwards in the form of branches (A) and these are called “stepped leaders”. They move downwars step by step to a height of 200 meters above the ground and stop. At that moment, positive charges called "upward streamers" are emitted from any object, building or structure on the ground and march towards the negative charged branches (B) in the sky.
One of the upward streamers meet with one of the stepped leaders and this forms an “ionized channel” (C) which is called "Lightning". All current inside the cloud flows through this ionized path following the structure body which emitted the upward streamer. During this electrical discharge, “unsuccessful” stepped leaders disappear like all other upward streamers and they shrink back to the ionized path to support the charge transfer.
Lightning seems as if it strikes only once, however it repeats many times in microseconds until the cloud completely neutralizes itself. Any of these strikes can create massive pressure and explosion effect with sudden rise in heat up to 3000 C. This is why structural damage and fire can oftenly seen at the points of lightning strikes. Lightning also damages electronic equipment directly and/or by its electromagnetic field. Lightning bolts can cause injuries and even deaths with a strike on a humanbeing.