The firing pin
safety is a passive safety
device that has been incorporated in most modern semi automatic pistols most notably in the Series 80 Mark IV m1911
It is a spring loaded nub that fits into a slot in the firing pin and prevents the forward movement of the firing pin unless the trigger is fully pulled back. This prevents an accidental discharge even if the loaded and cocked pistol is dropped on a hard surface. It is passive in the sense that there is no other manipulation that is needed to disengage it aside from pulling the trigger.
Some 1911 purists believe that this is sacrilege and that the added safety is not worth the subtle change in the smooth hair trigger pull characteristic of original Series 70 1911 pistols.
Fwiw, I have tried both and really can not tell if there is actually any difference, I suppose I have not yet reached the level where I can feel these subtle changes. It does add more moving parts to an already complicated machine.