- Freedom to use, that is the freedom to run the program, for any purpose (freedom 0).
- Help yourself which is the freedom to study how the program works, and adapt it to your needs (freedom 1). Access to the source code is a precondition for this.
- Help your neighbor that is, the freedom to redistribute copies without restriction (freedom 2).
- Help your community referring to the freedom to improve the program, and release your improvements to the public, so that the whole community benefits (freedom 3). Access to the source code is a precondition for this.
Source: Free Software Foundation