Trembling hand perfect equilibrium

In game theory, trembling hand perfect equilibrium, or simply perfect equilibrium, is a type of refinement of a Nash equilibrium that was first proposed by Reinhard Selten. A trembling hand perfect equilibrium is an equilibrium that takes the possibility of off-the-equilibrium play into account by assuming that the players, through a "slip of the hand" or tremble, may choose unintended strategies, albeit with negligible probability.

Source: Wikipedia — Trembling hand perfect equilibrium (CC BY-SA 4.0)