Q:

What is the scientific term form something that 'wraps around' a shape

I was wondering if there is a mathematical term for this: 
 
Imagine you had given the black shape - what does the red shape? I would call it, it wraps around the black one. 
Actually I am looking for a way to calculate / compute this. But i thought if i knew the name i would have more luck to google it.
Sorry for this vague description - Thanks for your help

A:

Convex hull ${{{{{{{{{{{{{{{}}}}}}}}}}}}}}}$

