I like this one: Simple version ....
... “free” as in “free speech,” not as in “free beer”. (From: http://www.gnu.org/philosophy/free-sw.html
More long-winded version ...
“Free software” means software that respects users' freedom and community. Roughly, the users have the freedom to run, copy, distribute, study, change and improve the software.
With these freedoms, the users (both individually and collectively) control the program and what it does for them.
Notice that nothing in the above mentions price being free. The goal here is to avoid another Microsoft/Apple monopoly of proprietary software allowing one company to rule. Hundreds of thousands of programmers all have access to the same code and all have the Freedom
to modify it to their needs. Of course, they may have to purchase it first ... but once they do they are free to manipulate it at will. The opposite of proprietary software today.
The software revolution is at hand. Major governments are switching to Open Source. Major corporations are switching to Open Source. It is now possible for any company to build a fully-functional enterprise on software that they have the entire code-base for and thus avoid being held hostage for the next 20 years in a licensing nightmare. And any company that still allows itself to be held hostage in that fashion will pay the price.
Long live GNU