Free software means software that respects the user’s freedom. There are four essential freedoms that the user of software should always have:
- Freedom Zero is the freedom to run the program however you wish.
- Freedom One is the freedom to study the source code of the program and to change it to make the program do what you wish.
- Freedom Two is the freedom to distribute copies of the program to others, when you wish. Now this includes republication of the program.
- And Freedom Three is the freedom to distribute copies of your modified versions to others when you wish, and this also includes publication if that’s how far you wish to go.
via Robin Good