The safest bonds are U.S. Government Bonds. They are backed by the full faith and credit of the government. Short term debt instruments, one year or less, are called Treasury bills. If the term of the original bond is 1 to 10 years, it is called a Treasury note. Debt issued for longer than 10 years is called a Treasury bond.
Corporations borrow money from investors, too.
They issue notes and bonds backed by the credit worthiness of the issuing company, which can be ascertained by checking the company's credit ratings. The higher the credit rating, the lower the interest rate yield. Municipal and state projects are frequently debt financed by municipal bonds. In order to encourage local and state governments to finance their own growth and development, Congress allows municipal bond interest to be received tax free for federal income tax purposes. You can reside in the state where the bonds are issued, and possibly even free of city taxes as is the case for New York City obligations held by New York residents.