Bonds are long-term securities with a maturity of greater than one year.  When you invest in a bond you are actually loaning money to an entity, be it a government, corporation, or other.  What you are buying when you purchase a bond is the debt of that entity and in return when the bond matures you will receive your principle plus the interest that has accrued throughout the period specified by the bond writer.  It is also possible to purchase some bonds where you can receive interest payments throughout the duration of the period of the bond.  Some of the common types of bonds are municipal bonds, US government, corporate, and foreign government issued bonds.