Double action or Double-action refers to one of two systems in firearms where the trigger both cocks and releases the hammer. For more information see Trigger (firearms).
Double-action only (DAO) firearms trigger: The trigger both cocks and releases the striker. There is no single-action function and the striker will return to its decocked position after each shot.
Traditional double-action– or double-action/single-action (DA/SA)– firearms trigger: The trigger combines the features of both a double-action only and a single-action only trigger. The firing mechanism automatically cocks the striker after the gun is fired. This mechanism will cock and release the striker when the striker is in the down position, but on each subsequent shot, and the trigger will function as a single-action.