The Cumulonimbus is forming from Cumulus congestus clouds, and may develop violent storms. The name comes from Latin and is composed by the reunion of two words: cumulo – heap, and nimbus – storm cloud.
It is a dense cloud, well developed vertically (from 200 to 6000 meters) and contains water in common form of ice, droplets or vapor.
The picture was made with a Canon PowerShot A550 camera, using these settings: exposure time – 1/1000 sec, focal length – 15.8 mm, ISO – 80, lens aperture – 4.5.