fork

   In  the  open-source  community,  a  fork is what occurs when two (or
   more)  versions  of  a  software  package's  source  code  are  being
   developed in parallel which once shared a common code base, and these
   multiple  versions of the source code have irreconcilable differences
   between  them. This should not be confused with a development branch,
   which  may  later  be folded back into the original source code base.
   Nor  should  it be confused with what happens when a new distribution
   of  Linux or some other distribution is created, because that largely
   assembles  pieces  than  can  and will be used in other distributions
   without conflict.

   Forking  is  uncommon;  in  fact,  it  is so uncommon that individual
   instances  loom  large in hacker folklore. Notable in this class were
   the  Emacs/XEmacs  fork, the GCC/EGCS fork (later healed by a merger)
   and  the  forks  among  the  FreeBSD,  NetBSD,  and OpenBSD operating
   systems.

[glossary]