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U
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| Unhinged - a stamp without
hinge marks, but not necessarily with original
gum. |
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| Unitrade Specialized Catalogue of Canadian Stamps - specialized stamp catalogue published by Unitrade Associates about every other year.
See Darnell.
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Unitrade catalogue |
| Universal Postal Union (UPU) - the UPU or Union Postale Universelle (its official title) originated and was first organized by Dr. Von Stephan of Germany, who convened the first conference of the General Postal Union (as it was at first named) at Berne on December 15, 1874. It was renamed the UPU in 1878. |
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| Unused - term that is normally applied to 'mint' specimens, but is equally applicable to one without gum, or to one that has been through the post and missed
cancellation. |
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| UPU - acronym for Universal Postal Union.
See above. |
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| Used - implies a stamp postally used, normally
cancelled, and in fair to good condition.
See Mint. |
 |
| Used on cover - implies that the stamp in question is on the original envelope, wrapper,
label, postcard, or other 'entire', and that it thus displays all the evidence for the philatelist or postal historian. |
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| UV lamp - ultra-violet lamp used for the detection of
fakes,
forgeries and
phosphor
tagged stamps. |

Ultra-violet lamps |
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