Definition from Nolo’s Plain-English Law Dictionary
A fee for the use of money. For example, you pay a bank or other creditor for lending you money or extending you credit. The interest rate represents the yearly price charged by the lender for the loan, expressed as a percentage of the total amount borrowed. You might be paid interest if you let a bank use your money--for example, by depositing it in a savings account. The bank pays you interest for the right to lend out your money (for which it receives interest from the borrower).