What is Smart?

I have never found a really good definition of how to define smart, though many refer to IQ as the measure of greatness. I have looked at a few IQ tests and the challenges provided by Mensa and certainly they measure some kind of intelligence related to solving difficult puzzles in a short period of time. What about someone with a photographic memory? Their mind could be full of interesting facts on all sorts of things, or they
could memorize a whole phone book. I knew someone back in college who reduced the calculus pre-med course requirement to cue cards and managed to get a perfect score in the course. He went on to be a successful doctor.
What about someone like Einstein – many considered the greatest mind of all time, yet he used to joke that he could not do simple fractions.
He was not much of a promising student, and after his doctorate could only find work as a patent clerk.

Lets take the scenario in which Einstein was never born, would we still have relativity and splitting of the atom today? I am wondering if he really changed history, and if so this could be a good way to define smart. But alas, I would argue that no. Many other scientists around his
time were quickly on his heels, and it’s likely that relativity would have been forumlated by someone else within the next few years anyway.
Maybe Eddington or Schwarzschild.
Science moves in increments. Look at the example of Newton – we give him credit for discovering differential calculus, but Laplace, Liebniz and others were not
far behind.

We can that Einstein did change the world by being the first to do something, like the first to climb mount Everest, or first to swim across the English channel. Being first gets you a place in history, being second may get you nothing. Yet what if these other people were just as smart, or smarter?

So what I am trying to get to is that there is probably no clear definition of smart, just some correlations. What we can agree on are those who did change the world.