A bond is a debt security, similar to an IOU. When you buy a bond, you are lending money to the issuer. In return for the loan, the issuer promises to pay you a specified rate of interest during the life of the bond and to repay the principal when it “matures,” or comes due.
In other words, a bond is a certificate representing the purchaser’s agreement to lend a business or government
money on the promise that the debt will be paid—with interest—at a specific time.
For US bonds:
A Treasury bond is government security issued in a term of 30 years. Investors buy Treasury bonds and then are paid interest every six months. When a Treasury bond matures, the owner is paid the bond’s par amount. Treasury bonds and U.S. savings bonds are not the same.