I really dislike the "safe"/"unsafe" terminology, there isn't a commonly-agreed upon definition of "safe". But I think it's safe to say that it's a combination

I really dislike the "safe"/"unsafe" terminology, there isn't a commonly-agreed upon definition of "safe". But I think it's safe to say that it's a combination of type and memory safety, not "low probability of having a defect". There certainly is a spectrum.