It might be a bit naive question, but I'm looking for an equation to describe a curve that looks like a typical cloud clipart icon. This is an example (not sure how to make it smaller): 
I think it could be something like epicycloid (particularly, ranunculoid), but I'm not sure how to make it more oblong.
To get those images, you could freely choose finitely many connection points forming a convex set and connect these connection points with smooth curves with positive (or negative) curvature.