A coin that has a faulty indentation made by the mint is called a brockage coin. A brockage coin occurs when a blank coin is inserted into the die, but not properly ejected. The coin is pressed again, but is either off center or has a second coin interfering.
Issues with brockage have occurred since ancient times. Examples of it can be found in early Greek and Roman coins. A brockage may increase the collectible value of a coin. The most sought after are coins that have a perfectly centered mirror image of the coin's opposite side. Increased mechanization in the minting process may have increased the frequency with which brockage now occurs.