Definition: A die crack is a mark appearing on a coin, usually in the form of a fine raised line or small blob. This happens because the coin die which struck the coin had a crack or small break in it that got transferred to the planchet during striking. Although most die cracks are considered a defect, some of them are collectable, such as the spiked head type.
Examples:
The coin was a wonderful specimen except for the die crack across the president's cheek.