When you buy U.S. bonds, you're lending money to the federal government. Bonds were used during World War I and II as a way for the federal government to raise money for fighting the wars. Still popular today, U.S. bonds can be purchased at banks.
Two kinds of U.S. Bonds
The money you invest in bonds is backed by the full faith and credit of the federal government. To learn about safety, risk, and interest rates, look at the Risk/Reward Pyramid.
How free are you to take your money out? This is long-range investing. Your money is tied up for years.
Interest rates are lower than some other investments because there's lower risk with bonds.