What is a greenback?

Greenbacks were paper currency issued by the United States during the Civil War, starting in 1861. They were called 'greenbacks' because of their green ink on the back. Unlike earlier forms of money, greenbacks were not backed by gold or silver but were considered legal tender by the U.S. government. The issuance of greenbacks helped finance the Union war effort but also led to inflation. Today, the term is sometimes used informally to refer to U.S. paper money in general.