UL - (Upper left) the upper left pane from a sheet containing four panes. "UL" is also used to describe plate blocks taken from the upper left corner of such sheets.

Ultraviolet (UV) - a wavelength of light just beyond the visible spectrum used to detect luminescence on tagged stamps and certain flaws on older stamps. There are two ends of the UV spectrum used to detect luminescence, short wave and long wave. Short wave is used to detect phosphor tagging and long wave to detect fluorescent tagging.

Uncatalogued -  the stamp is known to exist, and possibly listed in the catalog, but not priced

Underfranked - a cover bearing insufficient postage to prepay the service requested

Unexploded - a stamp booklet that is in the state in which it was sold by the post office, that is, not taken apart

Ungummed As Issued (UGAI) - stamps issued without gum, as opposed to stamps from which the gum has been removed. Many of the U.S. reprints and special printings were issued without gum.

Unhinged - a stamp without any hint of hinge marks, although not necessarily with original gum


Unique - Unique literally means "there is no other like it". We take exception to the usage "nearly unique".

United States Post Office Department (USPOD) - the branch of the government responsible for the operation of the Post Office. Upon its reorganization in 1971, the name was changed to the "United States Postal Service".

United States Postal Service (USPS) - an independent, self-supporting federal agency formed to run the Post Office, established on July 1, 1971, by the Postal Reorganization Act

The United States Specialist - the monthly journal of the United States Stamp Society, formerly known as the "Bureau Specialist". The U.S. Specialist is a veritable fountain of information for the U.S. collector.

United States Stamp Society (USSS) - the leading organization of collectors of U.S. stamps, formerly known as the BIA (Bureau Issues Association) http://www.usstamps.org/

Universal Postal Union (UPU) - an organization, founded in Berne, Switzerland in 1874 to regulate and standardize international postal usages and rates

Universal Stamping Machine Company - a major manufacturer of canceling machines from the 1900s to the 1990s

Unlisted - A stamp or other philatelic item not recognized by the catalog publishers.


Unofficial First Day Cover - a stamp on cover cancelled on the first day of issue, but from a city other than the one(s) in which the stamp was officially released

Untagged - a stamp printed without tagging. If this lack of tagging was unintentional the stamp is an error stamp, in the fullest sense a "missing color" error; it is simply missing a "color" that our eyes can’t see.

Unused - a stamp that has not been used for postage and therefore has no postmark. The stamp may have only partial or even no gum or may have been hinged so as to no longer be regarded as "mint". The terms "unused" and "mint" are often used interchangeably, but many would like to see the term "mint" reserved for stamps that have full, unhinged gum with bright and fresh color; stamps that are in the same condition as when they left the post office. A stamp may have gum that is not pristine or a lack of fresh and vibrant color, or any other fault for that matter and yet the stamp is still "unused" if it did not pass through the mails and does not have a cancellation.

Unwatermarked - stamps printed on paper without watermark, alternately, a stamp showing no watermark
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Upside-Down Jenny - the nickname for the error on the first U.S. Air Mail stamp issued, the twenty-four cent inverted U. S. airmail stamp of 1918, possibly one of the most famous stamps in the world
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UPU - an acronym for "Universal Postal Union"

UR - (Upper right) the upper right pane from a sheet containing four panes. "UR" is also used to describe plate blocks taken from the upper right corner of such sheets.

U.S. Automatic Vending Machine Company Perforations - perforations privately applied to imperforate stamps by the U.S. Automatic Vending Machine Company of New York for use in its vending machines, from 1906-1912.
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USCS - Universal Ship Cancellation Society. Founded in 1932, the UCSC is an international philatelic organization of over 1,500 members with an interest in postmarks and covers from all maritime services (www.uscs.org/).

Used - a stamp with either postal or revenue usage with a cancellation of some sort to note the fact

USIR - (United States Internal Revenue) a double-line watermark found on some revenue stamps. The USIR paper was inadvertently used to print three ordinary U.S. postage stamps, the six and eight cent stamps of the 1895 issue, Scott’s 281a and 282a, and the one dollar stamp of the 1938 issue, Scott 832b.
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USPOD - (United States Post Office Department) The acronym "USPOD" was also used to watermark paper used for U.S. postal cards from 1873-1875.

USPS - (United States Postage Stamp) the letters used to make the watermark used by the Bureau of Engraving and Printing on almost all U.S. postage stamps that had a watermark. The USPS watermark can be divided into two types, the double-line, from 1895 to 1910, and the single-line, late 1910 to 1914.
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USPS - (United States Postal Service) an independent, self-supporting federal agency formed to run the Post Office, established on July 1, 1971, by the Postal Reorganization Act.

U.S. Specialist - The monthly journal of the United States Stamp Society, formerly known as the "Bureau Specialist" (see United States Specialist above)