The low-altitude billowy cloud you're describing is called a cumulus cloud.

Here's why:

* Low Altitude: Cumulus clouds are typically found at low altitudes, below 6,500 feet.

* Billowy: Their characteristic shape is puffy, cotton-like, and often resembles a cauliflower.

* Other Features: Cumulus clouds are often associated with fair weather. However, they can develop into towering cumulonimbus clouds, which are associated with thunderstorms.

Let me know if you have any other cloud questions!