A bond, also known as fixed interest assets, is a form of debt security. Essentially, you are lending money to an entity in exchange for interest payments (or coupon payments), much like someone borrowing money from the bank and then paying interest on the borrowed amount. At the end of the contractually determined period, the principal amount will be paid back to you (the lender).
The rate of return for bonds is often quite lower in comparison to shares, however bonds tend to also be a much lower risk investment. As all investments there are still some associated risks.