A debt generally refers to something owed by one party, the borrower or debtor, to a second party, the lender or creditor. The lender or creditor can be a bank, credit card company, payday loan provider, or an individual. One country can also lend money to another country. Debt is generally subject to contractual terms regarding the amount and timing of repayments of principal and interest. The term can also be used metaphorically to cover moral obligations and other interactions not based on economic value. For example, in Western cultures, a person who has been helped by a second person is sometimes said to owe a "debt of gratitude" to the second person.
Interest is the fee charged by the creditor to the debtor. Interest is generally calculated as a percentage of the principal sum per year, which percentage is known as an interest rate, and is generally paid periodically at intervals, such as monthly or semi-annually.
Many conventions on how interest is calculated exist – see day count convention for some – while a standard convention is the annual percentage rate (APR), widely used and required by regulation in the United States and United Kingdom, though there are different forms of APR.