M - prefix letter used by 3M Corporation in front of the plate number on its modern stamp production.

*Machine Cancel - a cancellation applied by a machine, as opposed to one applied by a hand-held device.  Machine cancels were first used in the 1870s.

"Mail Early in the Day" - a slogan used as a marginal marking from 1966 to 1978.

Mail Stream - the movement of mail from the moment it is entrusted into the care of the Postal Service until it is delivered to its recipient.

Mailer’s Permit Postmark - a postmark applied to mail by a mailer prior to submission to the Postal Service.  Such private postmarks were first authorized in 1925.

Mailgram - a joint effort between Western Union and the USPS in which Western Union handled electronic transmission with hard copies delivered by the Postal Service.  The service is known to have been provided from 1972 to 1992.

Mailomat - a coin operated, self-service Pitney Bowes machine that imprinted a meter and retained mail for collection.  It was primarily used in the 1940s.

Mailometer Company - successor corporation to The Schermack Co.

Mailometer Perforations - see Schermack Perforations.

Mail Use Stamps - term used by the United States Postal Service for stamps intended for use on mail.

Main Post Office - the primary post office of a city that has secondary post office facilities.  Formerly known as General Post Office.

Make-shift booklets - see MDI booklets.

*Make-up Rate Stamp - a nondenominated  postage stamp, intended for use on first class mail, printed in anticipation of an increase in postal rates.  The stamp is equivalent in value to the amount of the increase.  Example: Weathervane stamp of 1998 (Scott 3257).

Manhardt-Alexander - subcontractor to Ashton-Potter (USA) LTD. for the printing of the 1994 lithographed American Music Series postage stamps (Scott 2854-2861).

Manila Paper - a coarse, light brown paper used in the manufacture of stamped envelopes.

*Manuscript Cancel - cancellation of a stamp by pen or marker.  Some early manuscript cancellations were applied by post offices with no cancelling device.  Modern manuscript cancellations are often applied in the field to stamps that escaped normal cancellation.  Stamps with manuscript cancellations are considered by some to be less desirable than stamps with other types of cancellations.

Maps - nickname for airmail stamps of 1926-1927 (Scott C7-C9) that include a map in their design.

*Margin - any printed or unprinted paper on a sheet or pane of stamps that does not contain a stamp.  Marginal markings are found in the margin.

Margin Block - any block of stamps with a margin attached.  Frequently, but not necessarily, a marginal marking will be found be found on a margin block.

*Marginal Marking - any intentional marking found on a plate except for the stamp itself.  Such markings will also appear on the printed sheet.  Examples of marginal markings include plate numbers, siderographer initials, Mr. Zip, and copyright notices.

Match and Medicine Stamps - see Private Die Proprietary Stamps.

Matrix - the waste produced by the process of die cutting.

MDI Booklets - hand made booklets produced by Minnesota Diversified Industries.  Most contained 15 water-activated gum  sheet stamps placed within blue cardboard covers having a rectangular opening through which the stamps could be seen.  By comparison, other MDI booklets contained self-adhesive stamps that were produced from pieces of web originally intended to be processed into convertible booklets.  With these booklets, special die cut mats were used to create booklet panes of 14, 15, or 16 stamps that were glued into the blue covers.

MeadWestvaco - Williamsburg, Pennsylvania based manufacturer of stamped envelopes from 1964 to 2008.

Mercantile Corporation - manufacturer of early twentieth century stamped envelopes and wrappers.

Merry Widow - nickname for the 1908 green Special Delivery stamp (Scott E7).

Meter - 1) a machine that imprints evidence of payment of postage.  2) the imprint of such a machine.

Micro-printing - extremely small words, or acronyms printed on some modern stamps as a security measure.

Middle West Supply Company - manufacturer of early twentieth century stamped envelopes and wrappers.

Miehle Press - 1) flat plate press first used at the BEP in 1894.  2) offset press used at the BEP in 1970s

Minnesota Diversified Industries - manufacturer of MDI booklets.

*Mint - a stamp in the same unused condition in which it came from the post office.  Sometimes this term is also applied to unused stamps that have been previously hinged.

Miscut - a freak that is created when a stamp or pane is not cut in the normal manner during the production process.

Misregistration - see registration.

Missionaries - a nickname for the 1851-1852 stamps of Hawaii.

Mixed Franking - 1) a cover bearing the stamps of two or more nations.  2) a cover with any other unusual combination of stamps used together, such as an Official and a definitive.

MOB - see Money Order Business Cancellation.

Mobile Post Office - post office facility that sorts and distributes mail while in transit, whether by rail (including street car), water, or highway.

Model - the final, approved drawing of a stamp.  It can be in the form of a drawing, a sketch, a photograph, a print or engraving, or any combination, or composite, of layers.

Money Order Business Cancellation - a circular handstamp cancellation containing the initials MOB; intended for use only on money orders but occasionally used on cover.

Morgan Envelope Company - manufacturer of nineteenth century stamped envelopes and wrappers.

Motor Vehicle Use Revenue Stamp - a revenue stamp paying the tax on the use of a motor vehicle.  Scott RV.

Mottled Tagging - tagging with an uneven, rough, or dappled appearance when viewed under ultraviolet light, as opposed to even or grainy tagging.  Some causes of mottled tagging are uncoated paper, worn tagging rollers, and offsetting of wet taggant ink when sheets are stacked.  Example: 1991 Dennis Chavez stamp, Scott 2186.

Mourning Cover - a cover with a black border, conveying news of a death.

MPO - see Mobile Post Office.

MPP - see Mailer’s Permit Postmark.

Mr. ZIP - a cartoon-like character used as a marginal marking from 1964 to 1986 promoting the use of ZIP Code.

Multi-Color Corporation - private printer of modern postage stamps.  Example: 19¢ Fishing Boat, Scott 2529.

*Multiple - a unit of two or more unseparated stamps.

*Mute Cancel - a cancel that does not include a date or time.  Generally used on Registered Mail and mail other than first class.

N               

Name Block - a block of stamps from the 1943-1944 Overrun Countries Issue (Scott 909-921) with a country name in the location where a plate number is customarily located.

Narcotic Tax Stamps - revenue stamps paying the federal tax on opium, coca leaves and their derivatives.  The tax was in effect from 1917 through 1971.  Scott RJA

National Air Mail Week - a campaign by the Post Office Department to promote air mail, conducted May 15-21, 1938, the twentieth anniversary of regularly scheduled air mail service.  A large variety of cachets and special flights were used in this observance.

National Bank Note Company - holder of the contract for printing postage stamps from 1861 to 1873.

National Bureau Precancels - BEP produced precancels with two parallel lines only and valid for precanceled mail at any U.S. post office.

*National Defense Issue - set of three postage stamps promoting national defense in 1940.  Scott 899-901.

National Label Co. - subcontractor to 3M for printing the 1994 Eagle stamp (Scott 2598).

*National Parks Issue - commemorative  postage stamp set of 1934 honoring various National Parks (Scott 740-749).  See also Farley's Follies.

National Postal Museum - a museum of the Smithsonian Institution, located in the old Washington City Post Office, housing the national postage stamp collection.

Nesbitt, George F. & Company - printer of stamped envelopes and wrappers from 1853 to 1870.

Never hinged - a stamp with gum undisturbed by the presence of a hinge.

*Newspaper and Periodical Stamps - stamps issued to document payment of postage on newspapers and periodicals.  From their release in 1865 until 1869 the stamps were affixed to wrappers on bundles, not to individual newspapers.  Beginning in 1875 stamps were placed in a receipt book.  These stamps were discontinued in 1898.  Scott numbers begin with PR.

Niagara Lithograph Company - the Buffalo, New York company that printed some of the 1917 documentary stamps for the Bureau of Engraving and Printing.

Nixie Clerk - a post office clerk responsible for handling items not readily deliverable because of a deficiency in address.

*Nondenominated Stamp - a stamp that does not have a value printed on its face, but often has an assigned value.  Such stamps often have a letter of the alphabet as part of their design that represents an assigned value.  Example: 1978 "A" stamp, Scott 1735, has an assigned value of 15¢.

Nonstandard Mail - First class mail weighing less than one ounce, and also of non-standard size or thickness.  An additional charge is imposed for nonstandard mail.

Nonstandard Postmark - A postmark created by a privately procured handstamp, i.e., one not supplied by the Post Office Department.

Number on number - a coil stamp with a plate number on the face and a back number on the back.

O               

Obliterator - a device that cancels a stamp; may also be called a "killer".

Occupation Stamps - see Allied Military Government Stamps.

OCR - see Optical Character Reader.

Oddity - a broad category of unusual variations.  Examples: stamps used before their first day of issue, errors in postmarks, and semi-official separations such as the Kansas City roulettes.

Off Center - a stamp whose design is not centered in relation to the edges of the stamp.

Off-line Perforator - a perforating device that is an independent machine; not an integral portion of a printing press.

Offices Abroad - a post office maintained on the soil of a foreign county.  Between 1919 and 1922 the U.S. Postal Agency in Shanghai, China was provided with surcharged postage stamps for use by that agency.

Offices in China - U.S. postage stamps surcharged for use by the U.S. Postal Agency in Shanghai, China.  Issued in 1919 and 1922.  Scott are prefixed with K.

Official Mail - mail sent by a government agency, using official stamps or a penalty envelope.

Official Postal Cards - postal cards issued for use by federal government departments.  Scott numbers are prefixed with UZ.

Official Stamped Envelopes - envelopes (and wrappers) used by federal government departments in the 1870s and early 1880s, and again beginning in 1983.  Scott numbers are prfixed with UO for envelopes and WO for wrappers.

*Official Stamps - stamps used by federal government departments in the 1870s and early 1880s, and again beginning in 1983.  Scott numbers are prefixed with O.  See also Postal Savings Mail.

Officially Sealed Label - See Seal.

Offset Lithography - see Offset Printing.

Offset Printing - a method of printing in which the inked image is first transferred from the printing plate to a rubber roller or blanket.  The inked image is then transferred from the roller to paper.  postage stamps were first printed from offset lithography in 1918-1920.  More recent stamps have been produced by a combination of offset and intaglio printing.  Offset printing is usually lithography, but not always.  For example, the Overrun Countries stamps were printed by offset letterpress, sometimes called dry offset or letterset.  The background colors on the 1968 and 1969 Christmas stamps (Scott 1363 and 1384) were printed by offset intaglio.

Open Mail - mid nineteenth century mail sent from an exchange office to an exchange office in another country for further processing and subsequent transmittal to another exchange office.

Optical Character Reader - postal equipment that "reads" the address on an envelope.  Sometimes this term is also used for the entire system, including the device that sprays the address on the envelope as a bar code.

Optiforma Press - six-color offset lithographic presses purchased from Goebel primarily intended to produce aerograms.

Orangeburg Coil - nickname for the rare 3¢ Washington-Franklin  coil with a vertical perforation gauge of 12 (Scott 389).  Used only by a drug company in Orangeburg, New York briefly in 1911.

Ordinary Stamps - see Definitives.

*Original Gum - gum on a stamp as issued by the post office.

Overall Tagging - Phosphor tagging that completely covers a stamp, as opposed to block tagging.  The clear taggant ink is applied on top of the stamp, as opposed to prephosphored paper tagging in which the taggant is in the paper itself.

Overland Mail - mid-nineteenth century mail that traveled across the U.S. by land.

*Overprint - printing placed on top of a stamp's face for some special purpose.  Overprints have been used for precancelling,  service inscription,  surcharging,  commemorative and security purposes, and on AMGs.  Example: Hawaii Sesquicentennial stamps (Scott 647-648).

*Overrun Countries - set issued in 1943-1944 honoring countries overrun during World War II.  Scott 909-921.