Call me stupid for asking, but what is "safe" here? I get the length-checked buffer copies and accesses, is there anything else? Less allowed type conversions?

You are talking about spatial safety. There are a few other types of memory safety:

- temporal safety (e.g. no use after free) - initialization safety (no read of initialized memory) - thread safety (no data races) - type safety (accessing memory with the correct type)

There is an old definition of language safety which means "no untrapped execution errors". It is not the only way to define safety, but it is a good way that you can adapt to various kinds of x-safety, such as memory safety.

I have a little post that explains this using a few more words, if interested: https://burakemir.ch/post/memory-safety-the-missing-def/