"Safe action" is
Glock's
prorietary firing mode for all of their pistols. It is different from
double action and
single action in that it is actually
somewhere in between.
Glocks do not have a hammer like traditional pistols but instead have a striker firing pin assembly. When the slide is racked on a glock with a charged magazine the backward movement of the slide puts a little tension on the striker spring and upon the forward movement to chamber a round this tension is kept in place. The gun is now practically in condition 2, but not quite.
Take note that the action of pulling the trigger on a glock will not just release the striker but also begin by increasing the tension on the striker spring before finally releasing it. On a glock, the trigger is also the sole controller as it alone takes care of disengaging the trigger safety, the firing pin safety and the builtin drop safety.
This design has made possible a pistol that can be safely carried with a round in the chamber without the aid of a manual safety yet still have a trigger pull weight comparable to that of a pistol in single action mode. It is only the trigger pull weight that is similar, the trigger travel though is still closer to that of a pistol in double action mode.