Starting at 2nd level, certain classes you can push themselves beyond their normal normal limits for a moment. If you are a Fighter, Wizard, or Rogue, on your turn you may take one additional Action (not Bonus Action) on top of your regular Action.

Once you use this feature, you must finish a short or long rest before you can use it again. Starting at 14th level, you can use it twice before a rest but only once on the same turn.