Free software license

Generally speaking, free software license is a phrase used by the free software movement to mean any software license that grants users of the software the following four freedoms:

The freedom to run the program for any purpose
The freedom to study and modify the program
The freedom to copy the program
The freedom to redistribute modified versions of the program

A license which preserves those freedoms for modified works is a copyleft license. See Free software movement for more information.

The Free Software Foundation maintains a list of free software licenses at their web site. The list distinguishes between free software licenses that are compatible or incompatible with the FSF license of choice, the GNU General Public License, which is a copyleft license. The list also contains licenses which the FSF considers non-free for various reasons. The list, which differs slightly from the open source license list, can be found at http://www.gnu.org/philosophy/license-list.html