P - prefix letter used by Ashton-Potter (USA) LTD. in front of the plate number on its modern stamp production.

Pacific '97 - one in a series of international stamp shows hosted once every decade in the U.S.  Held in San Francisco in 1997.  Stamps  (Scott 3130-3131) and souvenir sheets  (Scott 3139-3140) were issued in conjunction with this show.

Packet Letter - a letter carried by a ship operating on a regular schedule and under contract to the Post Office.

PAID - a marking applied to a stampless letter to indicate that postage had been paid in cash.

Paid Reply Postal Cards - two postal cards that are attached to each other and sold by the post office as a single unit.  One card is for sending a message.  The other is for the recipient to detach and send a reply.  Scott numbers begin with UY.

*Pair - two unseparated stamps.

PAL - see Parcel Airlift.

*Pan-American Issue - commemorative  postage stamps issued for the Pan-American Exposition in Buffalo in 1901.  Scott 294-299.

Panama Canal Zone - see Canal Zone.

*Pane - a unit of stamps cut from a full sheet, either for assembly into booklets, or for individual sale at post offices.  Sheets intended to be cut into panes for assembly into booklets will each produce a large number of relatively small panes, typically 30, 40, or 60.  Sheets intended for division into panes to be sold individually are divided into fewer but larger panes.  Many early sheets consisted of only two panes.  Most twentieth century sheets consisted of four panes.  Modern sheets consist of six or more panes.  Panes are commonly, but inaccurately, referred to by the public as sheets.

Pane-Position Diagrams - marginal marking first used in 1992.  This diagram identifies the position on a sheet from which the pane was cut.

Pantone Matching System - a popular color matching system used by the printing industry to print spot colors.  Most applications that support color printing allow specification of colors by indicating the Pantone name or number.

Paquebot - see Packet Letter.

Parcel Airlift - service for a fee that provides for air transportation, on a space available basis for mail on which the normal postage is paid, to or from military post offices outside the contiguous 48 states.  This service was popular during the Viet Nam conflict.  One special stamp was issued in connection with this service, Scott 1341.

*Parcel Post - the traditional name for the service for mailing most domestic packages, which began in 1913.  International Parcel Post was introduced in 1887.  Parcel Post is now a sub-category of Package Service, formerly Fourth Class Mail.

Parcel Post Postage Due Stamps - stamps used to account for postage due on parcel post mail, issued in 1913.  Scott numbers are prefixed with JQ.

Parcel Post Stamps - stamps issued for use on Parcel Post, beginning January 1, 1913.  Only these stamps could be used on Parcel Post until July 1, 1913, when any stamps could be used for Parcel Post, and Parcel Post stamps could be used as regular stamps.  Scott numbers are prefixed with Q.

Part Perforate - stamps on which at least one side is perforated as intended, and on which one or more sides are lacking any intended perforations.  Note: This term originally referred to properly perforated coil stamps that were not perforated on the two edges perpendicular to the perforations.  Such stamps were thus distinguished from imperforate coils.

Partial Plate Number - a less than complete plate number appearing on a traditional coil stamp, or on certain booklet panes.  These are freaks.  Plate numbers on these coils and booklet panes were generally trimmed off in the production process and were not regularly available.

Paste-up - the location on a flat plate  coil stamp (or, more commonly, on a pair or more of such stamps) where two sheets of flat plate stamps were pasted together.  Rolls of coil stamps were made from lengths of flat plate sheets that were 20 stamps long.  Thus a paste-up is normally found at 20 stamp intervals.

Paste-up Pair - a pair of coil stamps joined together by a paste-up.

Patent Cancellation - a cancelling device patented by the inventor.  These were popular in the period of the 1860s to 1880s.  In general, these devices operated by destroying, in some way, a portion of a stamp's paper.

Patent Lines - lines printed on the inside of a stamped envelope to guide writers in aligning the addressee’s name and address.

Patriotic Cover - a cover with a patriotic cachet, which was especially popular during the Civil War.

*Peak - the portion of a simulated perforation on a self-adhesive stamp that protrudes from the side of the stamp.

Pen Cancel - see Manuscript Cancel.

Penalty Envelope - an envelope sent free of postage by a government agency that contains a printed inscription, usually in the place where a stamp is customarily affixed, warning of a penalty for unauthorized use of the envelope.  Authorized in 1877.  Penalty envelopes are still used by the U.S. Postal Service but are obsolete for executive departments of the federal government.

Perf - see Perforation.

Perfecting - the process of printing inscriptions on the gum of some modern stamps by letterpress.

Perfin - (shortened form of "perforated initials" or "perforated insignia") a stamp with privately produced perforations through its face.  The perforations are generally in the form of initials or a symbol that identify the owner of the stamp.  Perfins are produced by businesses or organizations to discourage theft or misuse of their stamps.  Perfins were first made in 1908, and were most popular through the 1950s.  See Control Perfin.

Perforated Initials - see Perfin.

Perforated Insignia - see Perfin.

*Perforation - 1.) the rows of holes between stamps that enable easy separation of stamps.  The gauge (perforation size) has frequently changed.  For example, perf 15 was introduced in 1857, perf 12 in 1861, perf 10 in 1913, and perf 11 in 1917.  Other perfs have also been used.  "Perf" is a common contraction for perforation.  2.) the holes that were privately added by some private companies to help coil stamps pass through a vending or affixing machine.

*Perforation Gauge - 1) a number that equals the total quantity of perforation holes (or teeth) within the space of 20 mm.  For example, the Wildlife Conservation Issue of 1970 (Scott 1392) is said to have a perforation gauge of 11 x10 ½.  When referencing perforations, the horizontal perforation gauge is given first, and then the vertical. 2) a tool that measures the total quantity of perforation holes (or teeth) within the space of 20 mm.

Perforation Teeth - the tooth-like projections of paper on the edges of perforated  stamps.

Periodicals-Class Mail - the mailing classification for newspapers, magazines and other periodicals.  This classification was previously known as Second Class Mail.

Permit Mail Indicium - an imprint in the upper right hand corner of a cover indicating the authority, under permit, of a mailer to make large (bulk) mailings at a special (quantity) rate.

Persian Rug - nickname for the $200 and $500 revenue stamps of 1871.  Scott R132 and R133.

Personalized Computer Postage - postage purchased from an internet vendor and printed at a customer's convenience.

Personalized Postage - see Customized Postage.

Phantom Numbers - unintended, lightly printed plate numbers found in varying locations in the margins of sheets produced on the rotary press.  These are freaks caused by a set-off that occurs when the dryer on the press is not operating at a warm enough temperature.

Philatelic - pertaining to the hobby of collecting stamps,  postal stationery,  postal history, and related materials.

Philatelic Cover - a cover that is philatelic in origin, as opposed to a cover produced in the normal course of commercial or personal correspondence.

Philatelic Foundation, The - a leading organization in the expertization of stamps.

Philatelic Plate Number Association - predecessor organization to the United States Stamp Society.

Philatelic Truck Souvenir Sheet - a souvenir label, with no postal value, distributed by a post office truck that toured the nation from 1939 to 1941.

Philatelist - a stamp,  postal stationery,  or postal history collector.

Philippines - now independent country over which the U.S. exercised sovereignty from 1898 to 1946.  Overprinted U.S. stamps were used there beginning in 1899.  Beginning in 1906 the BEP printed stamps for use in the Philippines.

*Phosphor Tagging - a clear phosphor colloidal solution (taggant ink) applied over a stamp, or to its paper, or mixed with stamp printers' ink.  Tagging glows bluish-green or reddish when exposed to short wave ultraviolet light.  Reddish tagging was only used for air mail stamps from 1963 to 1978.  Beginning with the 1978 31¢ Wright Brothers (Scott C91-C92), bluish-green tagging was used for all subsequent air mail stamps.  Tagging has a brief afterglow that is used by automatic cancelling machines to find, face, and cancel an envelope's stamp.

Phosphored Ink - ink to which a clear taggant compound has been added.  Phosphored ink is infrequently used on stamps, but is frequently used for postal stationery.  Example of use of phosphored ink: Leif Erikson stamp of 1968, Scott 1359, and the Bicentennial envelope of 1976, Scott U582.

Photo essay - an essay in the form of a photograph.

Photogravure - see gravure.

Photogravure and Color Company - private printer of the 1967 5¢ Thomas Eakins Commemorative,  Scott 1335.

PhotoStamps - Personalized postage produced by Stamps.com.

(Bill) Pickett Stamp - see Legends of the West.

Pictorial Cancel - a cancellation that contains an illustration.

PictureItPostage - Personalized postage produced by Endicia.

Pigeon Blood Pink - a color found on a rare variety of the 3¢ 1861 stamp (Scott 64a).

Pink Backs - nickname for those Washington-Franklin stamps that "bleed" a pink coloration into the paper when placed in water.  This condition results from the use of inferior quality aniline ink.

*Pioneer Flights - air mail flights flown prior to the establishment of regularly scheduled air mail service.  The Pioneer Flight period is 1910-1916.

Pitney Bowes - the oldest supplier of postage meters (since 1920); manufacturer of mailing machines, inserters, cancelling machines, sorters and other postal equipment;  bought out Mailometer in 1924.

*Plate - the unit of a printing press from which stamps are actually printed.  19th and early 20th century stamps were produced from flat plates.  Beginning in the mid-1920s most stamps were produced from curved (180º) plates that were used in pairs on a rotary press.  Still more recently, many stamps have been printed from cylindrical plates.  A plate is sometimes also known as a printing base.

Plate Arrangement - see Plate Layout.

*Plate Block - a block of stamps, traditionally four in number, but sometimes more, which has a plate number printed on the attached margin.  Most collectors of plate blocks collect them in sizes as standardized by the Scott Catalogue.

Plate Cleaner - see Plate Finisher.

Plate Finisher - the employee of the BEP who removes extraneous lines or dots from an engraved plate after the siderographer has completed his job.

Plate Finisher Initials - marginal marking consisting of the initials of a plate finisher, punched into the plate, found in different locations on various plates before the location for them was standardized as the lower right corner.  These initials are known from 1909 until 1928.

Plate Flaw - a flaw in a printing plate that shows up on the corresponding sheet of stamps.  A plate flaw may be a crack or other defect that develops in a plate, or damage inflicted on a plate, such as an accidental dropping.

*Plate Layout - the layout of a plate; that is, the relationship of the elements on a plate, especially of the panes, to each other.

Plate Marking - any marking on a plate that is printed on the corresponding sheet.

*Plate Number - the numbers that appear on a printing plate.  These numbers are a part of the plate layout and most typically appear one or more times on each printed pane.  Numbers were once assigned to BEP-printed plates sequentially, in ever ascending order, with the same number never being assigned twice.  Such plate numbers appeared on sheets printed at the BEP from 1894 through 1980, when the practice was changed.  Beginning in 1980, plate numbers are Representative Numbers.

Plate Number Block - see Plate Block.

Plate Number Coil - see Coil Plate Number.

Plate Number Single - an individual stamp, mint or used, with a plate number attached.

Plate Printer Initials - see Printer's Initials.

Plate Proof - a proof printed (pulled) from a plate, as opposed to one pulled from a die.

Plate Sequence Number - A number engraved in the corner of the vignette and frame plates of the bicolored Pan-American issue of 1901 (Scott 294 and 295) to permit the same set of vignette and frame plates to be kept together on the press.

Plate Varieties - minor variations between apparently identical stamps that were printed from different plates.  Plate varieties can result from a damaged plate, or when there is some irregularity in the way a plate is made.  Plate varieties are constant, that is, as long as the variety appears on the plate, it will appear on every sheet produced from that plate.  More information about Plate Varieties may be obtained by referring to the Encyclopedia of Plate Varieties on U.S. Bureau-Printed Postage Stamps.

Plating - 1) the art of reconstructing a pane by determining the position of any given stamp on a pane.  Each position is assigned a consecutive number, beginning with the upper left corner and concluding with the lower right.  Plating is only done on early stamps where each stamp on a pane is unique due to minor variation.  2) the art of reconstructing a production-size sheet of certain booklet panes.

Playing Cards Stamps - revenue stamps issued from 1894 to 1940 to pay the federal tax on playing cards.  Scott numbers are prefixed with RF.

Plimpton Manufacturing Company - manufacturer of 19th century stamped envelopes and wrappers.

PMG - see Postmaster General.

PNC - abbreviation for Plate Number Coil.  See Coil Plate Number.

Pneumatic Mail - mail moved between post offices and railroad stations by pneumatic tubes in certain large cities, beginning with Philadelphia in 1893.  Pneumatic tube service was discontinued June 30, 1918.

POD - see United States Post Office Department.

Points down - the grill of a stamp, which, when viewed from the face, has the points of the grill directed downward.  Example: Scott 84.

Points up - the grill of a stamp, which, when viewed from the face, has the points of the grill directed upward.  Example: Scott 79.

Pony Express - mail service operated in 1860 and 1861 between St. Joseph, Missouri and Sacramento, California.  Local stamps were issued for this service by Wells, Fargo and Co.

Position - the place (location) on a printing plate from which a given stamp or pane was printed.

Position Blocks - blocks taken from various places on a sheet which show guide lines, arrows or other marginal markings.

Possessions and Administered Areas - foreign territories owned or administered by the United States, and for which the US issued stamps, including: Canal Zone, Cuba, Guam, the Philippines, Puerto Rico, and Ryukyu Islands.

*Post Card - a privately produced mailing card, as opposed to a Post Office produced postal card.  A post card does not have an indicium.

Post Office Department - see United States Post Office Department.

Post Office Seal - see Seal.

Post Road - a road, airway, waterway, or railway officially designated for the carrying of mail.

*Postage - the fee charged for sending an item through the mail.

Postage Currency - postage stamps affixed to or printed on treasury paper during the Civil War as a way of making stamps negotiable.  Scott numbers are prefixed with PC.

Postage Due Bill - a government generated form to which postage due stamps are attached.  It represents the amount of money owed by a postal customer, and frequently represents many individual pieces of business reply mail.

*Postage Due Stamp - a stamp indicating a deficiency in postage paid by the recipient.  First used in 1879.  Scott numbers are prefixed with J.

Postage Rate - the amount of money charged for postage.  See also Postal Fee.

*Postage Stamp - a piece of printed security paper, usually gummed, produced by the BEP or other authorized printer under controlled and secure conditions, sold by the Post Office, to be used by a mailer to document payment of postage.

Postage Validation Imprints - labels generated in post offices in conjunction with Integrated Retail Terminals (IRTs).  Postage Validation Imprints, which evidence payment of postage, replaced meters in post offices and first appeared in 1993.

Postal Buddy Machine - see Denominated Postal cards.

*Postal Card - a mailing card produced by the post office, as opposed to a privately produced post card.  A postal card has a stamp-like indicium.  Postal Cards were first issued in 1873.  Since 1999 Postal Cards have been sold for 1¢ over face value.  Scott numbers are prefixed with UX.  See also Denominated Postal Cards and Stamped Card.

Postal Convention - see Convention Rate.

Postal Envelope - see Stamped Envelope.

Postal Fee - the amount of money charged for a postal service, such as registered mail.

*Postal History - the study and collection of covers that chronicle the movement of the mails.  Desirable covers will have significant postal markings,  rates, routes, usages, origins and destinations.

Postal Insurance Stamps - stamps sold in a booklet of one stamp, from vending machines, to provide insurance on parcels.  Scott numbers are prefixed with QI.

*Postal Marking - any impression (whether by machine,  handstamp, or pen), placed on mail by an employee of the Post Office in the course of handling mail.

Postal Note Stamp - stamps used on Postal Money Orders.  Scott numbers are prefixed with PN.

Postal Savings Mail - official stamps issued in 1910 for use by the Postal Savings System.

Postal Savings Stamps - stamps issued by the Post Office Department, beginning in 1911, redeemable in the form of credits to Postal Savings Accounts.  Scott numbers begin with PS.

Postal Savings System - an interest paying savings system operated by the Post Office Department from 1910-1966.

Postal Service - see United States Postal Service.

*Postal Stationery - a category of products which includes Postal Envelopes,  Postal Cards,  aerograms,  wrappers, and international reply coupons.

Postal Transportation Service - successor to the Railway Mail Service in 1949 with responsibility for the transportation of mail by land, sea, and air.

Postal Treaty - see Convention Rate.

*Postmark - the impression made by the post office or authorized mailer on a cover, typically indicating the date, time and place of mailing.  Postmarks may be made by machine or handstamp.  Postmarks are most commonly circular, but are also found as ovals, boxes, straight lines and spray ons.  While postmarks are not cancels, they are sometimes used for that purpose, and the two terms are often and incorrectly used interchangeably.

Postmaster - the postal official in charge of a post office in a given locality.

Postmaster General - the chief executive officer of the old United States Post Office Department, and now of its successor, the United States Postal Service.

Postmasters' Provisionals - stamps and envelopes issued unilaterally by postmasters to meet local needs.  Scott numbers are prefixed with X (XU for envelopes).

POSTNET - U.S. Postal Service term for ZIP Code  barcode (acronym of POSTal Numeric Encoding Technique).

Potato Tax Exempt Stamp - stamp documenting exemption from tax under the Agricultural Adjustment Act.  Scott numbers are prefixed with RI.  See also Potato Tax Paid Stamp.

Potato Tax Paid Stamp - revenue stamp required by the Potato Act of 1935.  Because the Supreme Court quickly declared the act unconstitutional, these stamps were never used.  Scott numbers are prefixed with RI.  See also Potato Tax Exempt Stamp.

*Precancel - a postage stamp or revenue stamp that has been cancelled, under proper postal authority, before being affixed to mail (or taxable) matter.  Precancels are either Bureau Precancels or Local Precancels.  Some postal stationery has also been precanceled.

Predates - stamps or postal stationery  postmarked with dates prior to the official first day of issue.  These are not First Day Covers.

Prefix Letter - the letter preceding plate numbers on plates produced since the 1980s by private printers.  Each letter designates a specific private printer.  BEP plate numbers do not use a prefix letter.

Premiere Gravures - see August Issues.

Prephosphored Paper - paper that has taggant added during its production.  There are two types of prephosphored paper: Uncoated Paper and Coated Paper.  Uncoated paper tagging will be mottled.  Coated paper tagging may be grainy, mottled or even.

Preprinting Paper Crease - a stamp printed on paper that was creased at some point prior to printing.  When this crease is eventually opened up, an unprinted area becomes visible.  Preprinting paper creases are freaks.

Presentation Album - an album presented by postal authorities to a dignitary.  Examples are albums containing panes of newly released stamps presented at First Day Ceremonies, and the so-called "Roosevelt Albums" of small die proofs.

*Presidential Series - a series of sheet,  coil and booklet stamps, also known as Fifth Bureau Issue.  Most of the Presidential Series stamps were issued in 1938-1939.  Scott numbers begin at 803.

Presort Stamp - a postage stamp that documents the payment of postage on mail that is presorted, that is, mail bundled and prepared by the mailer in conformity with USPS standards.

Press (The) - private printer of modern postage stamps. Example: 45¢ Pumpkinseed Sunfish, Scott 2481.

Press Sheet - see Sheet.

Prestige Booklet - a booklet containing several face different stamps, descriptive text, and illustrations.  The first Prestige Booklet (Scott BK279) was issued in 2000 and honored U.S. Navy Submarines.

Prexies - see Presidential Series.

Printer's Initials - a marginal marking consisting of printer's initials, punched into an engraved plate by printers each time a printer printed from a plate.  The practice probably began in 1894.  It was discontinued in 1911 or 1912.  Printer’s initials were again used briefly in 1920 on some Washington-Franklin offset plates.

Printer's Waste - waste paper that is generated in the production of stamps.  Printer's waste is not a genuine error or freak.  It is simply waste paper intended for destruction and which can only reach the public through the illegal activity of an employee.  Some infamous printer's waste was stolen from the printer during the production of the 1995 Nixon commemorative.

Printing Plate - see plate.

Priority Mail - a subclass of first class mail, begun in 1968, providing a postage savings for items weighing 13 ounces or more.  The first stamp specifically intended for use on priority mail was the 1989 $2.40 Moon Landing stamp (Scott 2419).  The first stamped (prepaid) Priority Mail envelope was issued in 2003.

Private Aerogram - an aerogram (air letter sheet) privately printed, under permit, by a non-postal entity.  The air rate is correctly prepaid by postage stamp(s) as opposed to a stamp-like indicium.  Private aerograms are scarce, but are known from the Prexie and Liberty eras.

Private Coil - coil stamps produced by a private company from BEP printed imperforate  sheets, as opposed to those produced by the BEP.

Private Die Proprietary Stamp - a revenue stamp produced from a die and plate created at the expense of a private company and used exclusively by that private company.  The stamp was used to pay the tax on products sold by the company, and the stamps were generally affixed to the products sold.  The dies and plates were controlled by the BEP.  The categories of products that required these stamps were: medicines (Scott RS), matches (Scott RO), perfumes and cosmetics (Scott RT), playing cards (Scott RU) and canned goods (Scott RP).  Also see Proprietary Stamps.

Private Mailing Card - official term, used from 1898 until 1901, for what are now known as post cards.

Private Perforations - see Vending and Affixing Machine Perforations.

Progressive Die Proof - a proof made from a die that is not complete.  Such die proofs illustrate how work on a die progressed.  A progressive die proof is a special type of essay sometimes called a die essay or a "progressive essay".

Progressive Essay - see Progressive Die Proof.

Progressive Relief Break - see Relief Break.

*Project Mercury - the postage stamp honoring the 1962 orbital flight of John Glenn (Scott 1193).  The stamp was printed and shipped in secrecy, and released simultaneously at many post offices in the country upon Glenn's safe return to earth.

*Prominent Americans - definitive series of postage stamps appearing 1965-1981.  Scott numbers begin with 1278.

*Proof - an impression printed (pulled) directly from a die or a plate, usually done before production of stamps begins.  A proof is made to "prove" (approve) the engraving of the die, or the transfer to the plate.  Proofs are also pulled to enable engravers to see how their work on a die is progressing.  see Progressive Proof.  Proofs have been made as philatelic favors for dignitaries, sometimes years after the stamp was issued.  The BEP kept accurate records of all proofs that were made.  Proofs tend to have sharper images than the corresponding stamps.  Scott numbers for proofs contain a P.

*Proprietary Stamp - a revenue stamp documenting payment of federal tax on a commodity.  The government sold these stamps to many companies.  The categories of products requiring a proprietary stamp were: medicines, matches, perfumes and cosmetics, playing cards and photographs. See also Private Die Proprietary Stamps, which were produced exclusively for a single user.  Scott numbers are generally prefixed with RB although some are prefixed with R.

Provenance - the ownership history of a philatelic item.

Provisional Meter - a meter with a surcharge slug inserted to meet a temporary need.

Provisional Stamp - a stamp produced as an interim (temporary) measure to meet an immediate need.  Such stamps are often made by overprinting existing stamps.  Example: the first Cigarette Tubes Stamp (RH1), which is an overprint on a Documentary Stamp.

PTS - see Postal Transportation Service.

Puerto Rico - U.S. commonwealth that used provisional issues and overprinted U.S. stamps, stamped envelopes, wrappers, postal cards and revenue stamps.

Pulling - the process of printing a proof or other print from a die or a plate, as in the expression, "to pull a proof."

Punch Cancel - cancellation of a stamp by means of punching a hole.  Such cancels are generally found only on revenue stamps, although proofs are also found with punch cancels.

Punch Marks - marks made on an engraved plate using a punch tool.  Examples of such marks include printer's initials,  plate finisher's initials, "F", and stars.

Purvis Printing Company - overprinter of a small quantity of revenue stamps in 1898.

Putter-On-er - nickname for employees of the BEP who placed unprinted sheets of paper on the flat plate press.

PVI - see Postage Validation Imprints.