From the CCF Glossary (link on the left side):
double-struck
A condition that results when a coin is not ejected from the dies and is struck a second time. Such a coin is said to be double-struck. Triple-struck coins and other multiple strikings also are known. Proofs are usually double-struck on purpose in order to sharpen their details; this is sometimes visible under magnification.
double-struck
A condition that results when a coin is not ejected from the dies and is struck a second time. Such a coin is said to be double-struck. Triple-struck coins and other multiple strikings also are known. Proofs are usually double-struck on purpose in order to sharpen their details; this is sometimes visible under magnification.





















