Most people generally think that it means that there is a higher-level reality, and that there are beings within that higher-level reality engaged in creating our simulation. "Gods" for lack of a better word.

I prefer Greg Egan's interpretation in Permutation City, where simulations can become self-bootstrapping and that simulations need no "simulator" at all. No one's loaded universe.exe in some higher-lever reality, it runs itself.

That still won't stop me from attempting rowhammer attacks.