"Single-action" refers to a type of firearm mechanism where the trigger performs a single function: releasing the hammer or striker to fire the round. In this system, the hammer must be manually cocked before each shot, either by the shooter or through the action of the firearm. This design is commonly found in revolvers and some semi-automatic pistols. In contrast to "double-action" firearms, which can both cock and release the hammer with a single trigger pull, single-action requires an additional step. This distinction affects the speed and ease of firing, making single-action firearms popular among enthusiasts for their simplicity and precision.