"F" - a flat plate marginal marking, usually punched to the left of the upper right plate number, indicating that the plate had been hardened. This marginal marking is found most commonly on U.S. stamps from the 1920s and 1930s. The block at right has many interesting features. Since this was a "bi-color" stamp, the sheets were printed in two steps; first the black plate, #19737, which included the vignette as well as the letters "TOP", "F" and the plate number, and then the red plate, #19721, which also included an "F" to indicate the plate had been "finished" or hardened.  The "TOP" was to prevent the printer from inadvertently placing the sheets in the press upside down, and thereby creating an invert.

Face - the side bearing the printed design of the stamp, as opposed to the "back" of the stamp

Face Value - the postage value or denomination of a stamp. Most U.S. stamps issued after 1940 are not even worth face value in quantity. It is not uncommon to find "discount postage" lots at 15%-20% below face value.

Facsimile - a reproduction of a stamp or cover, produced with no intention to deceive. This is in direct opposition to a fake. 

Fake - a stamp, cover or cancel that has been produced to deceive a collector. The stamp at right is a Scott 78 chemically altered to look like the rare "Steel Blue", Scott 70b.

Famous Americans - the 1940 commemoratives honoring famous American authors, poets, educators, scientists, composers, artists, and inventors. See the First Day Cover entry below for an example of the Famous American stamp.
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Fancy Cancel - a collectible cancel that is either artistic or geometric in design

Farley's Follies - the nickname given to the 1935 special printing of stamps, in response to what was considered a lapse in judgment by Postmaster James Farley. When sheets of imperforate and ungummed commemoratives appeared on the philatelic market, the protests from U.S. collectors proved so great the Post Office was, in a sense, forced to issue these makeup stamps.
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Farwell Perforations - privately applied perforations to imperforate stamps by the Farwell Company for use in affixing machines, primarily made by the Schermack Company
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Fast Colors – colored inks resistant to fading when dipped in solvents and water


FDC - an acronym for "First Day Cover"

Fifth Bureau Issue - (Presidential Series of 1938) nicknamed "the Prexies", they were the fifth set of definitive postage stamps to be printed by the Bureau of Engraving and Printing
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Fifth International Philatelic Exhibition (FIPEX) - the fifth in a series of international stamp shows hosted in the U.S. once every decade. This one was held in New York City in 1956. As usual, a stamp, Scott 1076, and a souvenir sheet, Scott 1075, were issued in conjunction with the show.

First Bureau Issue (Triangles) - the first set of definitive postage stamps to be printed by the Bureau of Engraving and Printing. These issues are usually referred to as the "Triangles" of 1894 and 1895. The stamps from 1894 were printed on unwatermarked paper and the stamp from 1895 were printed on double-line USPS watermarked paper.
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First Day Cover - A First Day Cover consists of a stamp placed on an envelope and cancelled with the date the stamp was issued and with a postmark from the city in which it was issued. A distinction is usually made between covers with or without address and with or without cachet. Collecting First Day Covers is still an important part of many U.S. collector's collections.

First Flight Cover - a stamped envelope, with cancel and often with a descriptive cachet, flown on the inaugural of a new airmail route.

Flat Plate Press Plate Blocks - are most often collected in a plate number block of six with the plate number centered in the margin next to the middle stamp, as opposed to a rotary press plate block which is collected in a block of four with the plate number in the corner margin

Flown Cover - a cover that has been carried by air mail, and bears evidence of having been flown.

Flyspecking - the study of stamps of a particular issue with only minor variations

Folded Letter - a sheet of paper with the message written on the inside and folded over so that the name and address of the recipient could be written on the outside. The folded sheet of paper was sent without an envelope. The example at right is a folded letter sent on March 28, 1849, with a Scott #1 used for postage. The text of the letter was written above the reddish splotch at top and is not included here for space considerations. The red splotch is the remains of the wax used to seal the letter, removed when the letter was opened.

Foldover - the often dramatic stamp that results when the paper is folded over in either the printing or perforation process

Foreign Entry/Transfer - A foreign entry is the remnant of an original design or part of the design that was not completely removed from the plate before the new entry is made. Sometimes the incorrect design remains undetected as in the five cent rose Washington Franklin error stamps. 

Forgery - an imitation of a stamp or postmark intended primarily to deceive and defraud collectors. Sometimes forgeries are made to deceive postal authorities. These stamps are counterfeits and of course bring much stiffer penalties from postal authorities than do the forgeries intended to deceive collectors. The stamp at right is the imperforate stamp, Scott 344, with perforations added to make it look like a Scott 519.

Forwarding Agent - a person or entity, usually in a foreign city, who sends a piece of mail entrusted to him on to an addressee in the most expeditious manner. This was a service made obsolete by the formation of the Universal Postal Union.

Fourth Bureau Issue - the fourth set of definitive postage stamps to be printed by the Bureau of Engraving and Printing, often called the Series of 1922. The stamp at right is the eleven cent Hayes, the first denomination of the Series to be issued. The earliest printings tend to be bluer than the later printings; Johl called this shade "peacock blue", a description that, in the opinion of the editor, has all the romance and credibility of the "pigeon blood pink" of the three cent 1861 stamp. Scott lists this shade simply as "light blue".
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Foxing - orange brownish to dark brown stains on stamps or books caused by a fungus. Foxing is usually found in areas of high humidity, particularly in tropical climates. Storing stamps and books in air-conditioned rooms with controlled humidity may significantly retard foxing.

FPO - an acronym for "Fleet Post Office"

Fractional Usage (Bisect) - the use of a part of a stamp to pay the postage equal to less than the face value of the whole stamp. Although not always approved it was sometimes allowed when there was a shortage of stamps of the necessary denomination. Since a bisect or any other fraction of a stamp may be easily manufactured from the whole stamp, fractional usages are collected tied to a cover from a year and locale in which bisects were known to be used.

Frame - The frame is the part of the stamp design that surrounds the vignette, or central part of the design.

Franking - a marking on a cover, other than a stamp, that indicates that the postage has been paid

Freak - A freak is a mistake in the production of a stamp, such as color or perforation shifts, or over- or under-inking. Freaks are usually more common, less pronounced, and somewhat less collectible than "errors".

"FREE" - a handstamp bearing the letters "FREE" generally used on free franked mail

Free Frank - a marking indicating the right to send mail without payment of postage. Free postage is sometimes extended to government and military officials.

Front - the front part of a cover from which the back has been removed. The intact cover is known as an entire.

Fugitive Ink - any ink that tends to run when soaked in water or dipped in watermark fluid. Many postmarks are printed with fugitive inks and care must be taken lest the ink run and ruin the stamp or cover.