What does steel safe mean in the plastic mold building business?

Steel safe generally means that certain (component) features are integrated in the mold in such a way that tuning or modifications are possible after mold production. f.e. a snap should be tuned afterwards so no sliders etc. should be in the tuning zone f.e. sometimes the need for additional cooling is suspected, then the underlying mold area is made steelfsafe so that no other mold parts will be in the way of eventual cooling conduits.