An informal document that acknowledges a debt owed. IOU is an abbreviation, in phonetic terms, of "I owe you." The debt owed does not necessarily involve a monetary value but can also involve other products. With IOUs being informal, those issuing the IOU are given free reign when writing and issuing an IOU. Things like time, date, interest, and payment type are not mandatory but may be implied.


The informal nature of an IOU means that there may be some uncertainty about whether it is a binding contract, and the legal remedies available to the lender, as opposed to formal contracts like a promissory note or bond indenture. Because of this uncertainty, an IOU is generally not a negotiable instrument.

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