Richard Stallman, the creator of the movement for the Free software, he explains himself in this video What is free software, and makes a special analysis on why schools should only use Free software.
Free Software means, software that respects the freedom of the user and the social solidarity of their community […]
[…] That a program is Free Software means that the user has the four essential freedoms:
0. Zero freedom is the freedom to run the program however you want.
1. Freedom one is the freedom to study the source code of the program and change it so that the program does what you want.
2. Freedom two is the freedom to help others that is, the freedom to make and distribute exact copies of the program whenever you want.
3. Freedom three is the freedom to contribute to your community, that is, the freedom to make and distribute copies of your modified versions of the program.
With these four freedoms, the program is Free Software because the social system of its use and distribution is an ethical system, respecting the freedom of each one and respecting the community of users.
And all Software must be free because everyone deserves freedom. […]
It shows that Richard Stallman he thinks and lives as a computer scientist from the time he gets up until he goes to bed ... and the proof of this is that he begins to number the freedoms by zero :-)
A comment, leave yours
Why do you start listing the 4 freedoms from scratch?