Facing - identification mark which consists of a series of vertical bars read by automated postal equipment that identifies, orients, and separates various classes of mail
Facsimile - a likeness or imitation of a genuine stamp, marked in some way to denote its status so that it doesn't deceive a collector or defraud a postal administration. Catalog illustrations may be considered facsimiles.
Fake - a stamp, cover, or cancel that has been altered to appeal to a collector. In a broad sense, fakes include repairs, reperforations, and regummed stamps, as well as painted-in cancels, bogus cancels, or counterfeit markings.
Fancy (handstamp) - postmark with a decorative design
Fifth International Philatelic Exhibition (FIPEX) - The Fifth International Philatelic Exhibition was held in New York, April 28 to May 5, 1956.
First-day cover - a newly issued stamp affixed to an envelope and postmarked on the first day of sale at a city designated by the Post Office Department or Postal Service
Flat plate - a flat metal plate used in a printing press, as opposed to a curved or cylindrical plate
Flats - a postal processing term that stands for large envelopes, newsletters, and magazines. To be designated a 'flat', a mail piece must have one dimension that is greater than 6 1/8" high, 11 1/2" long, or 1/4" thick.
Fleet post office - an official U.S. post office for use by U.S. military naval units abroad
Flight cover - an envelope actually flown in the vehicle being commemorated
Folded paper - paper that is folded over at any time during the manufacturing processes. When unfolded, the paper will show a white space under the fold, and, conversely, may be printed on the back.
Foreign mail stamp - stamp issued specifically for use on mail going overseas. It is denoted by either the inscription or by the higher-valued currency used.
Forgery - a fraudulent reproduction of a postage stamp intended to deceive postal authorities and/or collectors
Franchise stamp - a stamp supplied without charge by postal administration to an individual or organization for distributing its mail
Franking - a mark on a cover that postage has been paid or that the envelope is being carried free of postage. Modern forms of franking are postage stamps and metered stamps.
Freaks - abnormal, usually non-repetitive occurrences in the production of stamps that results in a variation from the normal stamp but falls short of producing an error. Most paper folds, over-inking, and perforation shifts are freaks.
Free mail stamp - mail sent without a fee due to natural disasters. Troops on active duty might also enjoy this franking benefit.
Future delivery stamp - a stamp facilitating collection of tax on sale, agreement of sale, or agreement to sell any products or merchandise at any exchange board of trade, or other similar place for future delivery