7:   What is the real legal meaning of the GNU copyleft?

  The real legal meaning of the GNU General Public License (copyleft) will
  only be known if and when a judge rules on its validity and scope.  There
  has never been a copyright infringement case involving the GPL to set any
  precedents.  Please take any discussion regarding this issue to the
  newsgroup gnu.misc.discuss, which was created to hold the extensive flame
  wars on the subject.

  RMS writes:

    The legal meaning of the GNU copyleft is less important than the
    spirit, which is that Emacs is a free software project and that work
    pertaining to Emacs should also be free software.  "Free" means that
    all users have the freedom to study, share, change and improve Emacs.
    To make sure everyone has this freedom, pass along source code when you
    distribute any version of Emacs or a related program, and give the
    recipients the same freedom that you enjoyed.