Usury is the practice of making loans that are seen as unfairly enriching the lender. The term may be used in a moral sense—condemning taking advantage of others' misfortunes—or in a legal sense, where an interest rate is charged in excess of the maximum rate that is allowed by law. A loan may be considered usurious because of excessive or abusive interest rates or other factors defined by the laws of a state. Someone who practices usury can be called a usurer, but in modern colloquial English may be called a loan shark.

In finance and economics, interest is payment from a borrower or deposit-taking financial institution to a lender or depositor of an amount above repayment of the principal sum, at a particular rate. It is distinct from a fee which the borrower may pay to the lender or some third party. It is also distinct from dividend which is paid by a company to its shareholders (owners) from its profit or reserve, but not at a particular rate decided beforehand, rather on a pro rata basis as a share in the reward gained by risk taking entrepreneurs when the revenue earned exceeds the total costs.