Based on the World Meteorological Organization’s classification.
Cumulonimbus (Thundercloud)
Wikipedia: https://en.wikipedia.org/wiki/Cumulonimbus_cloud:
Cumulonimbus (from Latin cumulus ‘heaped’, and nimbus ‘rainstorm’) is a dense, towering vertical cloud,[1] typically forming from water vapor condensing in the lower tropospherethat builds upward carried by powerful buoyant air currents. Above the lower portions of the cumulonimbus the water vapor becomes ice crystals, such as snow and graupel, the interaction of which can lead to hail and to lightning formation, respectively. When occurring as a thunderstorm these clouds may be referred to as thunderheads. Cumulonimbus can form alone, in clusters, or along squall lines. These clouds are capable of producing lightning and other dangerous severe weather, such as tornadoes, hazardous winds, and large hailstones. Cumulonimbus progress from overdeveloped cumulus congestus clouds and may further develop as part of a supercell. Cumulonimbus is abbreviated Cb.
Cumulus (Fluffy clouds)
Wikipedia: https://en.wikipedia.org/wiki/Cumulus_cloud:
Cumulus clouds are clouds that have flat bases and are often described as puffy, cotton-like, or fluffy in appearance. Their name derives from the Latin cumulus, meaning “heap” or “pile”.[1] Cumulus clouds are low-level clouds, generally less than 2,000 m (6,600 ft) in altitude unless they are the more vertical cumulus congestus form. Cumulus clouds may appear by themselves, in lines, or in clusters.
Cumulus clouds are often precursors of other types of clouds, such as cumulonimbus, when influenced by weather factors such as instability, humidity, and temperature gradient. Normally, cumulus clouds produce little or no precipitation, but they can grow into the precipitation-bearing congests or cumulonimbus clouds. Cumulus clouds can be formed from water vapour, supercooled water droplets, or ice crystals, depending upon the ambient temperature. They come in many distinct subforms and generally cool the earth by reflecting the incoming solar radiation.