d (from the Latin denarius)— monetary symbol of penny or pence

Bisect — a stamp cut in half to denote half the original face value

Block of stamps — a unit of four or more unsevered stamps, including at least two stamps vertically and horizontally

Die — piece of metal with the engraved stamp design on it

Embossing — the process of pressing a die onto the paper’s surface to create a relief

Error — a mistake made in the production of a stamp or postal stationery

Essay — a design proposed for a stamp or piece of postal stationery but not adopted, or adopted only after alterations have been made

First day cover — an envelope bearing a postmark indicating that the stamp has been cancelled on the first day of issue

Forgery — an illegal copy

Hardening — a process by which the steel die is hardened 

Imperforate — a stamp without a perforated edge

Imprimatur — Latin for “let it be printed”. The first impression taken from an approved plate and given an official endorsement indicating that the plate may be used for printing stamps.

India paper — a thin, tough opaque printing paper of high quality, used primarily for die proofs

Jubilee — the celebration of the day on which an important event happened. A silver jubilee celebrates an event that occurred 25 years before; a golden jubilee, one that occurred 50 years before; and a diamond jubilee, one that occurred 60 years before.

Mulready — pictorial stationery issued in 1840 and named after artist William Mulready

Obliteration or cancel — a mark applied at the post office to indicate that a stamp has been used to pay postage

Overprint — something printed over the original design of a stamp

Perforation — holes cut between the stamps on a sheet so that they can be easily separated from one another

Plate — the basic printing unit placed on a press and used to produce stamps

Postmark — any official postal marking. Often refers to the mark that indicates the name of the post office and the date of mailing.

Proof — a trial impression taken from a die or plate 

Reprint — a stamp printed from the original plate after the issue has been withdrawn

Rouletting — the piercing of paper between stamps, usually as a series of slits. No paper is actually removed from the sheet, as in perforation.

“Silk” threads — pieces of “silk” used in the production of paper as an added security measure to prevent forgery

Specimen — a stamp bearing a “specimen” overprint indicating that it is not meant for official distribution

Watermark — security device or pattern, embodied in the paper to deter forgeries

Wove paper — a paper with a uniform texture produced by pressing pulp against a very fine netting