Series I refers to a type of U.S. savings bond designed to help individuals save money while earning interest. These bonds are issued by the U.S. Department of the Treasury and are available for purchase in electronic form. They are popular for their low minimum investment and the fact that they are backed by the U.S. government. The interest on Series I bonds is a combination of a fixed rate and an inflation rate, which adjusts every six months. This feature helps protect the purchasing power of the investment, making them an attractive option for long-term savers looking to hedge against inflation.