What type of error is this? It is one a $1 Silver Certificate

Chesspagan

Does anyone recognize this type of error? Some type of reverse overprint error?

Mike59

It’s called a wet ink transfer.
This explanation is from pmgnotes.com. “This type of error is basically a wet ink transfer. This occurs when the inked printing plate comes in contact with the impression cylinder. The impression cylinder presses the sheets into the printing plate. With the impression cylinder covered in ink, it now presses a mirror image of the design on the opposite side of a banknote. The offset printing can be partial or complete. When the front design is on the back of the note it’s called offset printing of front to back and vice versa.”
Very Cool error. Not worth allot but still a nice error.
Mike

Steve_in_Tampa

Exactly what @Mike59 said. 100% on point.
An alternative name for the error commonly used is “Offset”.