Dandy roll : A roller of mesh used in the manufacture of the paper which produces the watermark.

Definitives : Regular issues of postage stamps, usually sold over long periods of time. They tend to be fairly small and printed in large quantities often more than once.

Denomination : The postage value appearing on a stamp.

Die : The original engraved plate of the design of the stamp.

Die Cut : Scoring of self-adhesive stamps that allow a stamp to be separated from the liner.

Directory Markings : Postal markings that indicate a failed delivery attempt, stating reasons such as "No Such Number" or "Address Unknown."

Doctor Blade : A metal blade used to clean surplus ink from the cylinder or plate.

Double Transfer : The condition on a printing plate that shows evidence of a duplication of all or part of the design.

Duplicates : Extra copies of stamps that can be sold or traded. Duplicates should be examined carefully for color and perforation variations.