I see no one answered your question. I’m new to PF but think when there are no answers to a question that means the question is not worthy or is too difficult. For me, I think your question is worthy and too difficult but that never stopped me from answering as long as I admit up front that it is wobbly and for entertainment only. I am a retired engineer who early on found I was better at managing engineers than doing engineering so they made me the pointy haired boss. But I love science and especially physics.
If the object is a perfectly round then the outermost point is located everywhere on the surface and is called the “sphere” (as well as everything inside). For irregular shapes like a five sided polygon—I couldn’t find an answer. It may well be called, “The outermost point”. Really though, it should have a more techy name than that.