What is name of the notion described below.
Let S be any body (set of points) in Euclidian n-dimensional space.
Let H(S,r) be set of all points x that distance between x and y is <= r for some $y \in S$.
In other words, it is union all of spheres of radius r and centered in S.
What is name of this H(S,r) set. Is it r-Neighborhood of S ?