IOUs can be written horizontally or vertically. People used to write vertically, but now they mostly write horizontally. As long as the borrower signs the loan, it has legal effect. An IOU is a written document indicating the relationship between creditor's rights and debts, which is generally written and signed by the debtor, indicating that the debtor has owed the creditor the amount indicated in the IOU. An iou refers to a bill written to the other party when borrowing personal or public cash or goods, that is, an iou. After the money and goods were returned, the IOUs were revoked or torn up. This is a document. Usually used in daily life and business management.