Greenbacks are a term used to refer to paper currency issued by the United States government, particularly during the Civil War. They were called "greenbacks" because of their green ink on the back. Initially, these notes were issued to help finance the war and were not backed by gold or silver, leading to fluctuations in their value. Over time, greenbacks became a standard form of currency in the U.S. economy. In 1863, the National Banking Act established a system of national banks that could issue currency backed by U.S. government bonds, further stabilizing the value of greenbacks and integrating them into everyday transactions.