double action

"Double action" guns are much more common than single action - most semi-auto pistols are double-action, at least for the first shot. That means that pulling back the slide on your semiauto pistol only chambers the round - it doesn't "cock back" the striker pin. Only when the trigger is pulled beyond "first stage" (halfway back) does the hammer/striker become cocked. After that first shot, all other shots from the gun (until it is decocked, safety is activated, or you cycle through the rest of your ammo) are "single action," since the blowback from the previous shot provides the force to re-cock the weapon.