Simplify the following text for a Grade 7 native English-speaking person.
Original: The GNU Free Documentation License ( GNU FDL or simply GFDL ) is a copyleft license for free documentation , designed by the Free Software Foundation ( FSF ) for the GNU Project .
Simplified: The GNU Free Documentation License ( GFDL ) is a copyleft license for open content . It was made up by the Free Software Foundation ( FSF ) for the GNU project .