It's likely a poetic or descriptive phrase used to convey the idea of something being extremely soft and fluffy.
Here's how you could use it:
* "The baby's skin was as soft as a cloud, so delicate and smooth."
* "The marshmallow was as soft as a cloud, melting in my mouth."
Common idioms related to softness:
* As soft as butter: This idiom is used to describe something that is very soft and easily spreadable.
* As soft as velvet: This idiom describes something that is very smooth and velvety to the touch.
* As soft as down: This idiom refers to the softness of feathers, which are often associated with comfort and luxury.
While "as soft as a cloud" might not be a standard idiom, it effectively captures the feeling of something being incredibly soft and light.