This page is maintained by the Free Software Foundation's Licensing and Compliance Lab. You can support our efforts by making a donation to the FSF. Have a question not answered here? Check out some of our other licensing resources or contact the Compliance Lab at licensing@fsf.org.

The free software definition presents the criteria for whether a particular software program qualifies as free software. From time to time we revise this definition, to clarify it or to resolve questions about subtle issues. See the History section below for a list of changes that affect the definition of free software.

Free software means software that respects users' freedom and community. Roughly, it means that the users have the freedom to run, copy, distribute, study, change and improve the software. Thus, free software is a matter of liberty, not price. To understand the concept, you should think of free as in free speech, not as in free beer.

We campaign for these freedoms because everyone deserves them. With these freedoms, the users (both individually and collectively) control the program and what it does for them. When users don't control the program, we call it a nonfree or proprietary program. The nonfree program controls the users, and the developer controls the program; this makes the program an instrument of unjust power.

A program is free software if the program's users have the four essential freedoms:

A program is free software if it gives users adequately all of these freedoms. Otherwise, it is nonfree. While we can distinguish various nonfree distribution schemes in terms of how far they fall short of being free, we consider them all equally unethical.

The rest of this page clarifies certain points about what makes specific freedoms adequate or not.

Freedom to distribute (freedoms 2 and 3) means you are free to redistribute copies, either with or without modifications, either gratis or charging a fee for distribution, to anyone anywhere. Being free to do these things means (among other things) that you do not have to ask or pay for permission to do so.

You should also have the freedom to make modifications and use them privately in your own work or play, without even mentioning that they exist. If you do publish your changes, you should not be required to notify anyone in particular, or in any particular way.

The freedom to run the program means the freedom for any kind of person or organization to use it on any kind of computer system, for any kind of overall job and purpose, without being required to communicate about it with the developer or any other specific entity. In this freedom, it is the user's purpose that matters, not the developer's purpose; you as a user are free to run the program for your purposes, and if you distribute it to someone else, she is then free to run it for her purposes, but you are not entitled to impose your purposes on her.

The rest is here:

What is free software? - GNU Project - Free Software ...