(abbreviated DDO for obverse, DDR for reverse)
A doubled die occurs when a hubbing on a die is not in perfect alignment with previous hubbings, thus creating a "doubled" effect on the die. All coins made with this die have a doubled impression of the design transferred to them. There are many different effects which occur during striking which appear to the untrained eye as a doubled die.
The most sought after coin variety, the doubled die owes its fame to the Lincoln cent series. In 1955 the Philadelphia mint let a whopper of a doubled die pass through inspection. This coin, 1955-1DO-001, caused a craze in this country which is still felt to this day. Since the discovery of the now very valuable 1955 doubled die, there have been hundreds of other doubled die varieties found and cataloged, most notably by professional numismatist and coin attributor John Wexler. From Coppercoins.com Website
To learn more about Doubled dies and the different classifications of doubled dies. Click on the Coppercoins link below. Courtesy of Coppercoins.com