I thought this was profoundly cool:

In quantum mechanics one replaces the word 'orbit' with orbital, a word introduced by R.S. Mulliken who defined it in a simple way by saying that an orbital is as much like an orbit as quantum mechanics permits.

You see, Bohr's planetary model of an electron orbiting the nucleus (the iconic "atomic" symbol) was undone by Heisenberg. There can be no precisely defined position and energy for an electron as there is for a planet. It's a blur. So you can't really say that the electron orbits the nucleus even though you want to think that it does.  That's what Mulliken was trying to convey.