Baby Zepp (Baby Zeppelin) - ( Scott C18) a nick name for the 1933 50¢ Century of Progress air mail stamp, which portrays the Graf Zeppelin over the Atlantic Ocean with the Federal Building in Chicago at left and the hangar at Friedrichshafen at right. 

Back-of-the Book - stamps listed in the back of the Scott Catalogue following Postage Stamps. Starting with the Air Mail stamps, the Back-of-the-Book stamps begin their Scott number with a letter prefix.. 

Baker’s U.S. Classics - a compilation of weekly columns written for the "Stamps" magazine by Hugh and David Baker. The columns discuss all phases of U.S. classic material from stampless covers and rare U.S. stamps, 1845-1869, to foreign mails, with a smattering of data on the Civil War and the Confederates.

Bank Notes - the nickname for the stamps of 1870-1894 produced by the National Bank Note, Continental Bank Note, and American Bank Note Companies. The "large" Banknotes are listed in Scott as 134-218 and the "Baby" Banknotes as 219-229. 
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Barr-Fyke Machine Cancellation - the Barr-Fyke Machine Company of Kansas City, Missouri provided postal cancellation machines from about 1897 to 1905. The Barr-Fyke cancels are distinctive, and some bring a nice premium.

Barry Postal Supply Co. - of Oswego, N.Y., provided canceling machines from the 1890s until about 1910. A Barry cancel can often be identified by the slight impressions on the right edge created by pins that grabbed the letter as it passed through the machine. 

BEP - acronym for the "Bureau of Engraving & Printing". The Bureau of Engraving and Printing took over the printing of U.S. postage stamps in 1894 and continues to print stamps to this day.

BIA - an acronym for the "Bureau Issues Association" , an association of collectors to promote the study of the philatelic production of the Bureau of Engraving and Printing and of postage and revenue stamped paper produced by others for use in the United States and U.S. administered areas. 

Bi-color - a stamp printed in two colors.

Bisect - a half of a stamp which has been cut in two, usually by scissors or knife, to cover the postage of half the original face value. Bisects are commonly found with diagonal cuts and horizontal cuts, but occasionally with vertical cuts as well. Bisects were most often used to fill temporary shortages of the required denomination. Since a bisect genuinely used for postage often brings many times the value of the intact stamp, bisects are usually collected with the stamp tied by cancel to the original cover.

Black Harding’s - (Scott 610-613) commemorative/memorial stamps issued in 1923 to mourn the death of President Harding. Although, these stamps may look like the definitives of the era, they are not, they are commemorative stamps. 
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Black Jack - the nickname for the black two cent Andrew Jackson stamps and envelopes first issued in 1863
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Blind Perforations - an impression made by perforating pins in a place where perforations were intended, but from which the chads were not removed leaving the impression that no perf  hole is present. These interesting varieties are not to be confused with imperforate stamps. Blind perforations are considered freaks, not errors, and carry little, if any, premium over normally perforated copies.

Boardwalk Margins - stamps with large margins on all four sides, sometimes referred to as "jumbos". "Boardwalk margins" implies freakishly large margins.

Block - a multiple of stamps, generally four or more in number. A block may contain any number of stamps greater than four and need not be regular. For example a block of seven may have two rows of three stamps and one row of one stamp. It is unethical to break apart a block of stamps before about 1930 with the purpose of increasing the resale value of the lot, because it is destroying a piece of philatelic history. Blocks of stamps printed before about 1935 are becoming increasingly scarce, especially better centered blocks since the single well-centered stamps bring a premium. After 1935 many sheets of most stamps are still available, and with the advent of the electric eye are well-centered at that.

Booklet (Stamps) - one or more panes of stamps, sold by the post office, often in vending machines, usually with card covers and held together by staples, thread or glue. The booklet may be collected as an entire unit or by the pane.

Booklet Pane - a small block of stamps. Booklet stamps are collected as the entire booklet or by the individual pane. They are rarely collected in anything less than the entire pane, with single booklet stamps nearly always being far less collectible than even the regularly issued stamp with perforations on all four sides. Plate numbers are usually trimmed from the sheet before the booklet panes are cut, the pane at right is unusual, although not rare.

Brazer, Clarence W. - widely regarded as one of the great American philatelists, his book "Essays for U.S. Adhesive Postage Stamps" is considered essential reading for any serious student of U.S. stamps. 

Brinkerhoff Perforations - perforations privately applied to imperforate flat plate postage stamps by The Brinkerhoff Company for use in its vending machines.
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Broken Hat - the nickname for a plate variety on the two cent Columbian stamp of 1893, Scott 231, in which the third figure standing to the left of Columbus has a noticeable gap in his hat

Brookman’s - U.S. & Canadian Philatelic Price Guides – an alternative to the Scott catalog, most notable for the alternative numbering system in which commemorative and definitive issues are given individualized numbering systems.

Brookman, Lester - widely regarded as one of the great American philatelists, his books on 19^th Century U.S. stamps are considered essential reading and reference for any serious student of U.S. stamps. 

Bulls-eye Cancel - often called "socked-on-the-nose". A postmark that is struck directly or nearly directly on the center of the stamp. The cancel should be clean and legible.

Bureau Issue - a stamp produced by the Bureau of Engraving and Printing.

Bureau Issues Association (BIA) - originally the "Philatelic Plate Number Association" and now known as the "United States Stamp Society".

Bureau of Engraving and Printing - the division of the U.S. Treasury Department that took over the printing of U.S. postage stamps in 1894 and continues to print stamps to this day. Located in Washington, D.C., the Bureau printed nearly all U.S. stamps until the 1960s, but since 1967 has shared the printing duties with a variety of other companies.

Bureau Precancel - a precancel applied by the BEP in Washington D.C., as opposed to a precancel applied in the town for which the precancel applied.

Bureau Specialist - a monthly magazine originally published in 1930 by the BIA, dealing with all aspects of stamps issued by the Bureau of Engraving and Printing, but with a special emphasis on plate numbers and plate varieties. In 1966 the name was changed to "The United States Specialist" to reflect a broader scope.

Burnishing - an engraving term, it refers to the process of removing unwanted entries from an engraved printing plate. It is the diametrical opposite of hand tooling, which includes re-cutting, re-engraving and retouching.