Varieties vs. Errors
The terms variety and error are often used interchangeably. However, they are far different technically. To keep it simple, a variety is an occurrence that repeats exactly and en error is an occurrence that does not repeat exactly.
The confusion is often linked to the fact that some varieties are from a mistake and therefore people assume it's an error coin. Clear as mud? Examples forthcoming, I promise!
Both varieties and errors take place in one of three areas of the Mint. It happens in the planchet (or blank) making, during the die working process, or lastly during the striking process.
Regardless of how and why it happens, varieties and error coins are some of the most sought for by many collectors. In modern minting, neither happen often and it is far more likely to find these in older coins. However, it does still happen in modern coins and they too are prized by collectors.
A variety is an addition to a design that sets it apart and is repeatable. The 2008 Reverse of 2007 Silver Eagle pictured above is a good example of a variety. The only error that took place was the wrong reverse die was mixed in during striking. Another popular variety is the well known 1955 Doubled Die Penny. Look below and you can clearly see the doubling on the coin. The Silver Eagle variety occurred in the striking process, the penny in the die making process. However, varieties can also be on purpose as well. In 1878, the Mint made 8 tail feathers Morgan Silver Dollars and then started making a variety with 7 tail feathers to keep the eagle anatomically correct. All three of these are repeatable occurrences and by the very definition, varieties.