I have a set $S$ and a distance metric $d$, and I need the least upper bound on the distance between any two elements of the set:
$$ \inf \left\{ x: \forall a, b\in S, x \ge d(a, b) \right\} $$
I'm going to need to use this quantity a lot in a project I'm working on, so I want to be able to refer to it by some kind of reasonably short name. Is there an existing name for this quantity? If not, what would be a good name to use?