A common lesson in poker strategy — often picked up early on in a player’s education — is the one having to do with thinking on different “levels.”
Players who have learned how to think about not just their own cards, but about what their opponents are holding are said to be thinking on a higher level — exhibiting first- or second-level thinking (depending on where the counting of levels begins). Above that on the next-highest level are players who can further consider what their opponents think they have. And so on.
For most players, moving up each “level” in their poker thinking likely involves making several smaller “steps” along the way.