The Free On-line Dictionary of Computing (30 December 2018):

Birds Of a Feather

   (BOF) (From the saying "Birds of a feather flock together") An
   informal discussion group, scheduled on a conference program
   or formed ad hoc, to consider a specific issue or subject.  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.

   (1994-10-11)