The cost of borrowed money. It may be the payment you receive from an investment such as a bond, or the amount you pay for a loan, which is generally a percentage of the total amount borrowed. For example, if you take out a $5,000 loan for a year at 9% interest, the cost of taking the loan would be 9% of the total amount borrowed – $450. Also, the term interest can refer to a right or share in an asset or property.