There are different types of numismatic errors that can be made on a coin during the minting process. One type of error is a strike error. This happens when the planchet (the blank disc that will be struck as a coin) is struck. It is a manufacturing fault and often occurs when the coin's edge does not get struck with the rim image, usually because the collar die was absent. RPM is short for repunched mint mark. This error happens when the coin is struck twice, overlapping the first mark.

Another type of coin error, and one more valuable than the strike error is a die error. The die is one of the two metal pieces that are used to strike the sides of the coin. Because modern dies are made of steel which has been hardened, any error is hard to identify and usually quite rare, making these highly valuable to the collector.