An indent error occurs when two blanks are fed inadvertently into the same collar, with one blank partly overlaying on top of the other. When the hammer die strikes this combination, the upper blank will be forced into the lower blank, creating a depression which is shaped similar to the upper blank. A scarce type of indent occurs when a blank intended for one denomination lands on top of a blank from a different denomination.
Images courtesy of Byers
1894 Cent, 80% Indented Obverse,
ANACS MS-63 Brown (illustrated above).
Sources and/or recommended