A very quick electrical discharge that occurs between a cloud and the ground, between two clouds or within the clouds is called lightning. It can be seen as bright flash and is followed by the sound of the thunder.

The figure below shows the lightning between the cloud and ground.

The lightning frequency on earth is about 40-50 times a second.

The positive charges collect near the upper edge and the negative charges accumulate near the lower edge of the cloud and also near the ground. As the charge gets accumulated, its magnitude becomes very large and lightning occurs.