4 freedoms

Freedoms related to computer software:

0:The freedom to run the program, for any purpose

1:The freedom to study how the program works, and change it to make it do what you wish. Access to the source code is a precondition for this.

2:The freedom to redistribute copies so you can help your neighbor.

3:The freedom to distribute copies of your modified versions to others. By doing this you can give the whole community a chance to benefit from your changes. Access to the source code is a precondition for this

see http://www.gnu.org/philosophy/free-sw.html