From AMS Glossary
(Also called fair-weather cumulus.) A species of cumulus characterized by small vertical development, uniform flat bases and a general similarity among clouds.
Its vertical growth is usually restricted by the existence of a temperature inversion in the atmosphere; this in turn explains the unusually uniform height of the cloud tops of this cumulus species. A single cloud element that is able to penetrate the inversion may develop into cumulus congestus or even further to become cumulonimbus. As in all species of cumulus, wind shear with height may give rise to a hard appearance upshear, where cloud erosion in dry environment air is taking place, and a fuzzy appearance downshear . This species is unique to the genus cumulus.