Hero Point.

A player can spend a hero point whenever he or she makes an attack roll, an ability check, or a saving throw. The player can spend the hero point after the roll is made but before any of its results are applied. Spending the hero point allows the player to roll a d6 and add it to the d20, possibly turning a failure into a success. A player can spend only 1 hero point per roll. Each Long Rest recover one slot.