Which type of cloud is described as “fat and fluffy”?

The description of clouds as "fat and fluffy" aligns with cumulus clouds. These clouds typically have a puffy, cotton-like appearance and are often associated with fair weather. They form when warm, moist air rises and cools, leading to condensation in the upper parts of the cloud where the temperature is lower. This buoyancy gives cumulus clouds their characteristic fluffy shapes and can sometimes develop into larger storm clouds if atmospheric conditions are conducive.

In contrast, stratus clouds are generally more uniform and spread out, lacking the individual towering appearance characteristic of cumulus clouds. Cirrus clouds are thin, wispy, and high-altitude clouds that are not "fat" or fluffy; they are composed of ice crystals. Nimbus clouds refer more to a cloud's capability to produce precipitation rather than a specific shape or type, and they can encompass various forms, including some that are layered and not fluffy. Thus, cumulus clouds distinctly fit the "fat and fluffy" description.