IOU slips, also known as CHITS, are documents used to record a debt or promise of payment. They are typically written by the debtor and signed by both parties to acknowledge the debt. The term 'CHIT' is derived from the Hindi word for 'LETTER'. IOU slips are commonly used in business transactions, such as when a customer purchases goods on credit. They can also be used in personal transactions, such as when one person borrows money from another.