Definition: A partial mintmark that has not been completely abrade and inadvertently left on a working hub.

This 1997 Lincoln cent minted in Philadelphia shows the remnants of a D mint mark. It has been surmised that the Philadelphia mint ran out of obverse dies and had to abrade the mintmark from a working hub to produce more working dies. The second upper image to the right shows the partial D mintmark indicated by the white arrow.

The lower left image is of a 1997 D Lincoln cent with that image being overlayed in the lower image to the right. When the two images are compared, the remnants of the D mint mark fall right in place of where that mintmark should have been.