Technically, bills, notes, and bonds are all bonds. They are all backed by the full faith and credit of the U.S. government. They are all issued electronically (you don’t get a fancy piece of paper as you do with savings bonds). They can all be purchased either directly from the Treasury or through a broker. They can all trade like hotcakes.
The major difference among them is the time you need to wait to collect your principal:
Treasury bills have maturities of a year or less.
Treasury notes are issued with maturities from two to ten years.
Treasury bonds are long-term investments that have maturities of 10 to 30 years from their issue date.
Keep in mind that you don’t have to hold any of these securities (bills, notes, or bonds) till maturity. You can, in fact, cash out at any point. The longer until the maturity of the bond, however, the more its price can fluctuate and, therefore, the more you risk losing money.