IOU refers to the act of borrowing in the name of an individual, which belongs to the category of personal debt. Personal debts are generally formed in the form of written IOUs, but only IOUs that meet the prescribed format can be used as legal documents to collect arrears. Generally, it is written and signed by the debtor, indicating that the debtor has owed the creditor the debt with the amount indicated in the IOU. Also known as "IOUs", its legal basis is contract law and other related civil laws.

An iou is a practical voucher written by an individual or unit when borrowing personal or public cash and property. IOUs can be divided into two categories from the perspective of issuing documents. One is the IOU or IOU written to the other party when an individual borrows money or things from others or units; The other is a voucher iou written by the unit when it borrows money from individuals or other units. The most common use of "IOUs" is that when borrowing cash, lenders often ask borrowers to issue "IOUs" when delivering loans and give them to lenders to confirm the borrowing facts; When borrowing goods, sometimes the lender will ask the other party to make a "debit note".