I know this is an extremely specific thing to need a name for, and I don't expect that one already exists, but is there a reasonable name that might be applied to the idea?
I would also like a term for the opposite possibility, for the relation holding between vertices A and B such that there is at least one vertex from which A is reachable but B is not.
Thanks in advance if you can help me find reasonable terms for these concepts.
EDIT: I'm referring here specifically to some vertex other than A and B themselves. I failed to make that clear initially.