1. [common] Abbreviation for the phrase “Birds Of a Feather” (flocking together), an informal discussion group and/or bull session scheduled on a conference program. It is not clear where or when this term originated, but it is now associated with the USENIX conferences for Unix techies and was already established there by 1984. It was used earlier than that at DECUS conferences and is reported to have been common at SHARE meetings as far back as the early 1960s.
2. Acronym, “Beginning of File”.