RARELY USED GREENBACK is a term used to describe a TWO-dollar bill, which is rarely seen in circulation. The TWO-dollar bill was first issued in 1862 and has been issued intermittently since then. It is the least circulated denomination of paper currency in the United States, with only 1.2 billion bills in circulation as of 2018. The TWO-dollar bill is still legal tender and can be used for any transaction. Despite its rarity, it is still a valid form of payment.