It means that the contract you enter when you loan money has limitations to what you can use said funds for, and how or what it's secured with (including interest). It would seem that the creditors of Bankman-Fried gave him quite liberal limits, if it wasn't simply the byzantine structure of his many, many straw companies that made it extremely hard to understand what the money was ever used for, so much so that he may or may not have lost track himself.