Double Action (DA / DA-SA)
A trigger that both cocks and releases the hammer in one pull — heavier and longer than single action, often paired as DA/SA.
A double-action trigger performs two jobs in a single press: it cocks the hammer and then releases it. That makes the first pull longer and heavier, which many consider a safety advantage for carry. A pure double-action-only (DAO) gun fires every shot that way, while a DA/SA pistol fires the first shot double-action and subsequent shots single-action as the slide re-cocks the hammer.
DA/SA designs (think Beretta 92, SIG P226, CZ 75) give a deliberate first shot and lighter follow-ups, at the cost of managing two different trigger feels and often a decocker. Revolvers are commonly double-action, letting you either stage a long press or thumb-cock for a lighter single-action shot.