'Cumulus' is specifically used in meteorology to describe a type of cloud formation.

Weather Related

Cumulus clouds are distinct for their puffy, cotton-like appearance which can be associated with fair weather.

Physical Appearance

'Cumulus' refers to the shape, not the color; they can turn gray when rain is about to fall.

Not Always White

'Cumulus' can be used metaphorically to describe an accumulation of any tangible things.

Metaphoric Use

Using 'cumulus' in non-meteorological contexts often evokes a visual image of a pile mimicking cloud shapes.

Visual Imagery

'Cumulus' implies a large accumulation, not just a small stack or few items gathered.

Scale of Accumulation

 cumulus, heap or pile, and stratus, layer or sheet. But that wasn't the clever part. Clouds are constantly changing, merging, rising, falling, and spreading throughout the atmosphere, rarely maintaining the same shapes for more than a few minutes.

How did clouds get their...

 to feel that we can really ever experience life by watching it on a computer screen, you know, when we're in a wi-fi zone. But the one cloud that best expresses why cloudspotting is more valuable today than ever is this one, the cumulus cloud.