Bonds are a form of loan.
They are issued by governments or companies with the aim of raising capital to cover their expenses or investment plans. The bond issuer is the equivalent to a borrower, while the bond holder is the equivalent to a lender. However, a bond is different to a loan, as it depends on market supply and demand fluctuations, and not on bank intermediation.
Bonds are issued for a specific time no less than 1 year and have a specific issue value. This value, also known as face value, is equal to the amount the issuer is borrowing. This is also the amount the investor receives at bond maturity. If the investor chooses to sell their bond before maturity, they receive its current market value.
Depending on the bond type and terms of issue, interest (coupon) payments are made on a regular basis. This is why bonds are also known as fixed-income securities.