to print one colour on top of another to obtain a third colour
Any printing that is done on an area that has already been printed.
Any inscription printed on a regular iissue stamp in addition to its original vignette usually denoting a change of government, in a war, commemorate events, propaganda, etc.
When printing separations, an option where overlapping colors are printed in their entirety instead of knocking out. Overprinting eliminates the possibility of color gaps between objects, but can result in unacceptable color shifts. Overprinting can be used to add the appearance of a third spot color to a document.