[chatmasta]

The problem is the word "safe," which is inherently ambiguous. Safe from what? A better term would be "correct," because at least that implies there is some spec to which the developer expects the program to conform (assuming the spec itself is "correct" and devoid of design flaws).

[RHSeeger]

While I agree with your point in general, I don't think the choice of wording is "the problem" here. But I do agree your wording is more correct.

It is almost impossible to prove a program is "correct". But things like memory safe languages, static typing, and automated tests allow us to prove the ways in which it is not "incorrect". And the more places it is not incorrect, the more likely it is to be correct (even if we can't prove it).