Debt is money owed by one party, the borrower or debtor, to a second party, the lender or creditor. The borrower may be a sovereign state or country, local government, company, or an individual. The lender may be a bank, credit card company, payday loan provider, business, or an individual. Debt is generally subject to contractual terms regarding the amount and timing of repayments of principal and interest. A simple way to understand interest is to see it as the "rent" a person owes on money that they have borrowed, to the bank from which they borrowed the money. Loans, bonds, notes, and mortgages are all types of debt. 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.
The English term "debt" was first used in the late 13th century. The term "debt" comes from "dette, from Old French dete, from Latin debitum "thing owed," neuter past participle of debere "to owe," originally, "keep something away from someone," from de- "away" (see de-) + habere "to have" (see habit (n.)). Restored spelling [was used] after c. 1400. The related term "debtor" was first used in English also in the early 13th century; the terms "dettur, dettour, [came] from Old French detour, from Latin debitor "a debter," from past participle stem of debere;...The -b- was restored in later French, and in English c. 1560-c. 1660." In the King James Bible, various spellings are used; the spellings "detter [are used] three times, debter three times, debtor twice and debtour once." 
Interest is the fee paid by the borrower to the lender. Interest is calculated as a percentage of the outstanding principal, which percentage is known as an interest rate, and is generally paid periodically at intervals, such as monthly or semi-annually.
Interest rates may be fixed or floating. In floating-rate structures, the rate of interest that the borrower pays during each time period is tied to a benchmark such as LIBOR or, in the case of inflation-indexed bonds, inflation.
There are many different conventions for calculating interest. Depending on the terms of the debt, compound interest may accumulate at a specific interval. In addition, different day count conventions exist, for example, sometimes each month is considered to have exactly thirty days, such that the interest payment due is the same in each calendar month. The annual percentage rate (APR) is a standardized way to calculate and compare interest rates on an annual basis. Quoting interest rates using APR is required by regulation for most loans to individuals in the United States and United Kingdom.
For some loans, the amount actually loaned to the debtor is less than the principal sum to be repaid. This may be because upfront fees or points are charged, or because the loan has been structured to be sharia-compliant. The additional principal due at the end of the term has the same economic effect as a higher interest rate.
Riskier borrowers must generally pay higher rates of interest to compensate lenders for taking on the additional risk of default. Debt investors assess the risk of default prior to making a loan, for example through credit scores and corporate and sovereign ratings.
There are three main ways repayment may be structured: the entire principal balance may be due at the maturity of the loan; the entire principal balance may be amortized over the term of the loan; or the loan may partially amortized during its term, with the remaining principal due as a "balloon payment" at maturity. Amortization structures are common in mortgages and credit cards.
Debtors of every type default on their debt from time to time, with various consequences depending on the terms of the debt and the law governing default in the relevant jurisdiction. If the debt was secured by specific collateral, such as a car or home, the creditor may seek to repossess the collateral. In more serious circumstances, individuals and companies may go into bankruptcy.
Common types of debt owed by individuals and households include mortgage loans, car loans, and credit card debt. For individuals, debt is a means of using anticipated income and future purchasing power in the present before it has actually been earned. Commonly, people in industrialized nations use consumer debt to purchase houses, cars and other things too expensive to buy with cash on hand.
People are more likely to spend more and get into debt when they use credit cards vs. cash for buying products and services. This is primarily because of the transparency effect and consumer’s "pain of paying." The transparency effect refers to the fact that the further you are from cash (as in a credit card or another form of payment), the less transparent it is and the less you remember how much you spent. The less transparent or further away from cash, the form of payment employed is, the less an individual feels the “pain of paying” and thus is likely to spend more. Furthermore, the differing physical appearance/form that credit cards have from cash may cause them to be viewed as “monopoly” money vs. real money, luring individuals to spend more money than they would if they only had cash available.
Besides these more formal debts, private individuals also lend informally to other people, mostly relatives or friends. One reason for such informal debts is that many people, in particular those who are poor, have no access to affordable credit. Such debts can cause problems when they are not paid back according to expectations of the lending household. In 2011, 8 percent of people in the European Union reported their households has been in arrears, that is, unable to pay as scheduled "payments related to informal loans from friends or relatives not living in your household".
A term loan is the simplest form of corporate debt. It consists of an agreement to lend a fixed amount of money, called the principal sum or principal, for a fixed period of time, with this amount to be repaid by a certain date. In commercial loans interest, calculated as a percentage of the principal sum per year, will also have to be paid by that date, or may be paid periodically in the interval, such as annually or monthly. Such loans are also colloquially called "bullet loans", particularly if there is only a single payment at the end – the "bullet" – without a "stream" of interest payments during the life of the loan.
A syndicated loan is a loan that is granted to companies that wish to borrow more money than any single lender is prepared to risk in a single loan. A syndicated loan is provided by a group of lenders and is structured, arranged, and administered by one or several commercial banks or investment banks known as arrangers. Loan syndication is a risk management tool that allows the lead banks underwriting the debt to reduce their risk and free up lending capacity.
A company may also issue bonds, which are debt securities. Bonds have a fixed lifetime, usually a number of years; with long-term bonds, lasting over 30 years, being less common. At the end of the bond's life the money should be repaid in full. Interest may be added to the end payment, or can be paid in regular installments (known as coupons) during the life of the bond.
A letter of credit or LC can also be the source of payment for a transaction, meaning that redeeming the letter of credit will pay an exporter. Letters of credit are used primarily in international trade transactions of significant value, for deals between a supplier in one country and a customer in another. They are also used in the land development process to ensure that approved public facilities (streets, sidewalks, stormwater ponds, etc.) will be built. The parties to a letter of credit are usually a beneficiary who is to receive the money, the issuing bank of whom the applicant is a client, and the advising bank of whom the beneficiary is a client. Almost all letters of credit are irrevocable, i.e., cannot be amended or canceled without prior agreement of the beneficiary, the issuing bank and the confirming bank, if any. In executing a transaction, letters of credit incorporate functions common to giros and traveler's cheque. Typically, the documents a beneficiary has to present in order to receive payment include a commercial invoice, bill of lading, and a document proving the shipment was insured against loss or damage in transit. However, the list and form of documents is open to imagination and negotiation and might contain requirements to present documents issued by a neutral third party evidencing the quality of the goods shipped, or their place of origin.
Companies also use debt in many ways to leverage the investment made in their assets, "leveraging" the return on their equity. This leverage, the proportion of debt to equity, is considered important in determining the riskiness of an investment; the more debt per equity, the riskier.
Governments issue debt to pay for ongoing expenses as well as major capital projects. Government debt may be issued by sovereign states as well as by local governments, sometimes known as municipalities.
The overall level of indebtedness by a government is typically shown as a ratio of debt-to-GDP. This ratio helps to assess the speed of changes in government indebtedness and the size of the debt due.
The debt service coverage ratio is the ratio of income available to the amount of debt service due (including both interest and principal amortization, if any). The higher the debt service coverage ratio, the more income is available to pay debt service, and the easier and lower-cost it will be for a borrower to obtain financing.
Different debt markets have somewhat different conventions in terminology and calculations for income-related metrics. For example, in mortgage lending in the United States, a debt-to-income ratio typically includes the cost of mortgage payments as well as insurance and property tax, divided by a consumer's monthly income. A "front-end ratio" of 28% or below, together with a "back-end ratio" (including required payments on non-housing debt as well) of 36% or below is also required to be eligible for a conforming loan.
For example, in mortgage lending in the United States, the loan-to-value concept is most commonly expressed as a "down payment." A 20% down payment is equivalent to an 80% loan to value. With home purchases, value may be assessed using the agreed-upon purchase price, and/or an appraisal.
A debt obligation is considered secured if creditors have recourse to specific collateral. Collateral may include claims on tax receipts (in the case of a government), specific assets (in the case of a company) or a home (in the case of a consumer). Unsecured debt comprises financial obligations for which creditors do not have recourse to the assets of the borrower to satisfy their claims.
Credit bureaus collect information about the borrowing and repayment history of consumers. Lenders, such as banks and credit card companies, use credit scores to evaluate the potential risk posed by lending money to consumers. In the United States, the primary credit bureaus are Equifax, Experian, and TransUnion.
Debts owed by governments and private corporations may be rated by rating agencies, such as Moody's, Standard & Poor's, Fitch Ratings, and A. M. Best. The government or company itself will also be given its own separate rating. These agencies assess the ability of the debtor to honor his obligations and accordingly give him or her a credit rating. Moody's uses the letters Aaa Aa A Baa Ba B Caa Ca C, where ratings Aa-Caa are qualified by numbers 1-3. S&P and other rating agencies have slightly different systems using capital letters and +/- qualifiers. Thus a government or corporation with a high rating would have Aaa rating.
A change in ratings can strongly affect a company, since its cost of refinancing depends on its creditworthiness. Bonds below Baa/BBB (Moody's/S&P) are considered junk or high-risk bonds. Their high risk of default (approximately 1.6 percent for Ba) is compensated by higher interest payments. Bad Debt is a loan that can not (partially or fully) be repaid by the debtor. The debtor is said to default on his debt. These types of debt are frequently repackaged and sold below face value. Buying junk bonds is seen as a risky but potentially profitable investment.
Bonds are debt securities, tradeable on a bond market. A country's regulatory structure determines what qualifies as a security. For example, in North America, each security is uniquely identified by a CUSIP for trading and settlement purposes. In contrast, loans are not securities and do not have CUSIPs (or the equivalent). Loans may be sold or acquired in certain circumstances, as when a bank syndicates a loan.
Loans can be turned into securities through the securitization process. In a securitization, a company sells a pool of assets to a securitization trust, and the securitization trust finances its purchase of the assets by selling securities to the market. For example, a trust may own a pool of home mortgages, and be financed by residential mortgage-backed securities. In this case, the asset-backed trust is a debt issuer of residential mortgage-backed securities.
Central banks, such as the U.S. Federal Reserve System, play a key role in the debt markets. Debt is normally denominated in a particular currency, and so changes in the valuation of that currency can change the effective size of the debt. This can happen due to inflation or deflation, so it can happen even though the borrower and the lender are using the same currency.
Some argue against debt as an instrument and institution, on a personal, family, social, corporate and governmental level. Islam forbids lending with interest even today. In hard times, the cost of servicing debt can grow beyond the debtor's ability to pay, due to either external events (income loss) or internal difficulties (poor management of resources).
Debt will increase through time if it is not repaid faster than it grows through interest. This effect may be termed usury, while the term "usury" in other contexts refers only to an excessive rate of interest, in excess of a reasonable profit for the risk accepted.
In international legal thought, odious debt is debt that is incurred by a regime for purposes that do not serve the interest of the state. Such debts are thus considered by this doctrine to be personal debts of the regime that incurred them and not debts of the state. International Third World debt has reached the scale that many economists are convinced that debt relief or debt cancellation is the only way to restore global equity in relations with the developing nations.
Excessive debt accumulation has been blamed for exacerbating economic problems. For example, before the Great Depression, the debt-to-GDP ratio was very high. Economic agents were heavily indebted. This excess of debt, equivalent to excessive expectations on future returns, accompanied asset bubbles on the stock markets. When expectations corrected, deflation and a credit crunch followed. Deflation effectively made debt more expensive and, as Fisher explained, this reinforced deflation again, because, in order to reduce their debt level, economic agents reduced their consumption and investment. The reduction in demand reduced business activity and caused further unemployment. In a more direct sense, more bankruptcies also occurred due both to increased debt cost caused by deflation and the reduced demand.
At the household level, debts can also have detrimental effects — particularly when households make spending decisions assuming income will increase, or remain stable, in years to come. When households take on credit based on this assumption, life events can easily change indebtedness into over-indebtedness. Such life events include unexpected unemployment, relationship break-up, leaving the parental home, business failure, illness, or home repairs. Over-indebtedness has severe social consequences, such as financial hardship, poor physical and mental health, family stress, stigma, difficulty obtaining employment, exclusion from basic financial services (European Commission, 2009), work accidents and industrial disease, a strain on social relations (Carpentier and Van den Bosch, 2008), absenteeism at work and lack of organisational commitment (Kim et al., 2003), feeling of insecurity, and relational tensions.
Global debt underwriting grew 4.3 percent year-over-year to US$5.19 trillion during 2004. It is expected to rise in the coming years if the spending habits of millions of people worldwide continue the way they do.
Traditions in some cultures demand that debt be forgiven on a regular (often annual) basis, in order to prevent systemic inequities between groups in society, or anyone becoming a specialist in holding debt and coercing repayment. An example is the Biblical Jubilee year, described in the Book of Leviticus.