Which type of cloud is characterized by a rounded mass accumulation?

The type of cloud characterized by a rounded mass accumulation is cumulus. Cumulus clouds often form in fair weather and have a distinct fluffy appearance, resembling cotton balls. They typically develop due to rising warm air that cools and condenses at higher altitudes, creating puffy, well-defined cloud formations.

Their vertical development can indicate weather changes, as cumulus clouds can grow into larger cumulonimbus clouds, which are associated with thunderstorms. In contrast, stratus clouds usually produce a uniform gray layer across the sky, lack the pronounced vertical structure seen in cumulus clouds, and primarily blanket the sky rather than accumulate in defined shapes. Cirrus clouds are thin, wispy clouds found at high altitudes, lacking the rounded appearance altogether, while nimbus clouds specifically refer to rain-bearing clouds that can belong to various cloud types, including nimbostratus or cumulonimbus.