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.