Levelling
Also: leveling, levelling war, level 3 thinking
Thinking about what your opponent thinks you have, and what they think you think they have — layers of reasoning stacked on top of each other. A 'levelling war' is two players out-guessing each other until the reasoning eats itself.
Level one is 'what do I have', level two 'what does my opponent have', level three 'what does my opponent think I have', and so on. The practical rule is to think exactly one level above your opponent: against a player who only looks at their own cards, elaborate bluffs are wasted, and against a thinking player a straightforward value bet can be a trap. 'Getting levelled' means talking yourself out of the obvious play because you credited the opponent with more thought than they gave.