The Jargon File (version 4.4.7, 29 Dec 2003):

BOF
 /B·O·F/, /bof/, n.

    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”.