Die defect

A die defect is a unique and unintentional flaw in a coin die and is created through excessive use or polishing of the die. A die bearing such a defect is occasionally referred to as a defective die. Generally, and depending upon the magnitude of the defect, coins that are produced from these dies are considered error coins. Also, the term encompasses a wide variety of design errors that were engraved into the die originally and were slipped into circulation before the incorrect design was discovered.