Common Belief
A group of people has ‘Common Belief’ of ‘p’ when each person in the group believes each person in the group believes each person in the group believes [sic.] ’p’. This is independent of whether they personally believe ‘p’.
E.g.: The “Emperor’s New Clothes” is a story about Common Belief and its collapse: each townsperson believes everyone else believes everyone else believes [sic.] they can see the invisible fabric, up until the moment the kid shouts the King is naked, and everyone realizes everyone else is thinking the same thing.