Backstamp - A handstamp applied to the back of a letter, usually indicating date of transit or receipt at the office of destination.
Back of the Book - Stamps that are normally listed in the back of the catalog, after the regular stamp issues. This might include airmail, special delivery, semi-official, official, postage due, local issues, stamped envelopes, postal cards, essays, and revenue stamps.
BAPO - British Army Post Office
Battal postmark - Rectangular postmark used in several parts of the Turkish Empire in 1863–4, showing the word "Battal" i.e. "Cancelled" surrounded by dots.
BFPO - British Force Post Office
Bilingual - Postage stamp or postmark, printed in two languages.
Bisect - A stamp cut or perforated into two parts, each half representing half the face value of the original stamp. Officially authorized bisects have often been used during temporary shortages of commonly-used denominations. Some countries have, at times, permitted trisects or quadrisects.
Boîte - (French) Letterbox.
Bogus - Fraudulent postage stamp that pretended to have been issued, but never was. Sometimes either belonging to a non-existent issue or a non-existent country.
BM - Boîte Mobile – (French) Mobile Box, Traveling Post Office; in Holy Land philately, BM cachets applied to letters collected from the ship's mail box and later handed over to the French Postal Authority at the nearest port for onward transmission.
Booklet - Small, convenient book containing panes (pages) of mint postage stamps (and often slogans or advertisements).
Booklet Pane - Complete pane (page) of postage stamps (plus slogan or
advertisement labels, if any) from a booklet, preferably with selvedge.
Boxed postmark - Type of cancelling device used by the Turkish Empire after 1865, generally the name of the locality in Arabic script enclosed by double or triple frame with or without rounded corners.
BPO - Branch Post Office.
Burelage - Design of fine, intricate lines printed on the face of security paper, either to discourage counterfeiting or to prevent the cleaning and reuse of a stamp. The burelage on some stamps is part of the stamp design.
Birken - "Postal Stationery" - "Handbook of Turkish Philately, Part I - Ottoman Empire - Andreas Birken" - 1995