Success is the most loosely defined, illogical concept in the startup world. When your friends are raising big rounds, you think they are successful, even though most of them won't survive beyond the runway that round gives them (esp. at that stage).

Yet the media and the community celebrates founders for all sorts of things and call it "success" when it's not. So yes, it's incredibly vague, and the existence of an accounting formula means nothing in the founder psyche.