one step "above" what is expected daily in the profession. So, if a business casual the professional expectation, you wear a suit. But if jeans and golf shirt are the professional expectation, you might wear slacks, shirt, and blazer.
The idea being that you dress "up," but not too far up.
If someone from the company were giving a presentation to other professionals in their field, how would they dress? That's probably how you want to dress for the interview.