U

U: Envelope or Letter Sheet. Scott catalog number prefix to identify stamps other than standard postage.
U: Used
U A: Unaddressed
U A E: United Arab Emirates.
UC: Air Post Envelope or Letter Sheet. Scott catalog number prefix to identify stamps other than standard postage.
UCS,UT: Unitrade Specialized Canada Catalog
UDC: Undated Circular Cancel
UHISABI: Term for Charity on Estonian Christmas seals.
UL: Upper Left
ULTRAVIOLET (UV): Lamp that gives off two different wave lengths-Shortwave and Longwave. Shortwave UV light will highlight phosphor tagging, either in the printing ink or the coating on a stamp. Longwave UV light will spot fluorescence in the paper of a stamp or cover.
UNADDR: Unaddressed
UNDERPRINTS: A security device where a color, design or pattern is printed on the paper before the stamp design is applied.
UNGUMMED: Stamps without any gum as issued.
UNHINGED: Stamps without any traces of hinge marks.
UNIQUE: Auction term meaning no other like it.
UNISSUED: A stamp that has been prepared for use but not issued.
UNIT WATERMARK: An arrangement so that a complete design appears on every sheet of paper.
UNITED NATIONS (UN): The banding together of nations of the world to strive for peace and understanding. UN stamps are sold in the UN Building in New York, Geneva and Vienna and have postal validity throughout the world.
UNIVERSAL POSTAL UNION (UPU): Organized in Berne, Switzerland in 1874 to regulate and standardize international postal usages and rates.
UNL: Unlisted
UNOFFICIAL FIRST DAY CANCEL: Cancels applied on the first day but not in the first day of issue city.
UNOFFICIAL PERFORATIONS: Perforations done upon issuance of a stamp to help separate the stamps such as the Confederate issues and private vending machine coils.
UNOFFICIAL REPRINTS: Stamps reprinted at a later date from the original plates but not by the original issuing entity.
U N P A: United Nations Postal Administration.
UNUSED: A stamp in mint condition as purchased from the post office. Also can mean a stamp that has no gum or is regummed.
UNWATERMARKED: Stamps printed on paper that has no watermark.
UO: Official Envelope. Scott catalog number prefix to identify stamps other than standard postage.
U P U: Universal Postal Union
UPSIDE DOWN JENNY: The 1918 24-cent U. S. airmail with upside down Jenny aircraft.
UR: Upper Right
USED: A stamp that has been "used" to pay postage, bears a cancellation or defacing mark.
USED ABROAD: Stamps of another country used in a nation or colony which already has its own stamps.
U S P O D: United States Post Office Department, official branch of the government for delivering the mail until 1971, when it became the USPS.
U S P S: United States Postal Service. Established by the Postal Reorganization Act of July 1, 1971 as an independent, self-supporting federal agency within the Executive Branch.
U S S S: United States Stamp Society, formerly the Bureau Issues Association.
UX: Postal Card. Scott catalog number prefix to identify stamps other than standard postage.
UXC: Air Post Postal Card. Scott catalog number prefix to identify stamps other than standard postage.
UY: Paid Reply Postal Card. Scott catalog number prefix to identify stamps other than standard postage.
UZ: Official Postal Card. Scott catalog number prefix to identify stamps other than standard postage.