Freedoms of Open Source Software

The Free Software Foundation, headed by Richard Stallman, supports the idea that software should be free, which entails the following:

• The freedom to run the program, for any purpose (freedom 0).
• The freedom to study how the program works, and adapt it to your needs (freedom 1).
• The freedom to redistribute copies so you can help your neighbor (freedom 2).
• The freedom to improve the program, and release your improvements to the public, so that the whole community benefits. (freedom 3).

These four freedoms define the core of the GNU GPL (General Public License), under which a good part of software for Linux is licensed today.
— FreshMeat, Dec 18th 1999