What is a Double Die Coin?

By GovMint :

A double die coin, often referred to as a doubled die coin, is a numismatic treasure sought after by collectors for its unique characteristics. This phenomenon occurs during minting when the die used to strike the coin impresses the design onto the coin multiple times in slightly misaligned positions. As a result, elements of the design appear doubled or overlapping, creating a distinct visual effect on the coin. Though they are technically considered mint errors, double die coins are appealing to collectors for their intriguing appearance and the intricacies of their production process, making them prized additions to any coin collection.

Sources Used:

https://www.thesprucecrafts.com/doubled-die-coins-768451