Is innocent until proven guilty a law?

Excuse me, could you clarify something for me? The phrase "innocent until proven guilty" is often cited in legal discussions and proceedings. But, is it actually a law in itself, or is it more of a principle that guides the legal system? I'm wondering if there's a specific statute or code that explicitly states this, or if it's rather a fundamental principle embedded within the broader framework of legal reasoning and due process. Could you elaborate on this point?