I am really new on here so please forgive me if this has been asked before. I have searched to see if this has been asked but I couldn't find it on the search.

I am playing as standard tuning, I have heard of the expression to down tune half or full. What does this really mean? I know that it has to do with tuning down but to what scale? If someone can tell me this, I really appreciate it.

Thank you

Malcolm