``Free software'' is a matter of liberty, not price. To understand the concept, you should think of ``free speech'', not ``free beer.''
``Free software'' refers to the users' freedom to run, copy, distribute, study, change and improve the software. More precisely, it refers to four kinds of freedom, for the users of the software:
A program is free software if users have all of these freedoms. Thus, you should be 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.
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.
You may have paid money to get copies of GNU software, or you may have obtained copies at no charge. But regardless of how you got your copies, you always have the freedom to copy and change the software.
In order for these freedoms to be real, they must be irrevocable as long as you do nothing wrong; if the developer of the software has the power to revoke the license, even though you have not given cause, the software is not free.
However, certain kinds of rules about the manner of distributing free software are acceptable, when they don't conflict with the central freedoms. For example, copyleft (very simply stated) is the rule that when redistributing the program, you cannot add restrictions to deny other people the central freedoms. This rule does not conflict with the central freedoms; rather it protects them.
Rules about how to package a modified version are acceptable, if they don't effectively block your freedom to release modified versions. Rules that ``if you make the program available in this way, you must make it available in that way also'' can be acceptable too, on the same condition. (Note that such a rule still leaves you the choice of whether to make the program available or not.)
In the GNU project, we use ``copyleft'' to protect these freedoms legally for everyone. But non-copylefted free software also exists. We believe there are important reasons why it is better to use copyleft, but if your program is non-copylefted free software, we can still use it.
See Categories of Free Software (18k characters) for a description of how ``free software,'' ``copylefted software'' and other categories of software relate to each other.
Sometimes government export control regulations and trade sanctions can constrain your freedom to distribute copies of programs internationally. Software developers do not have the power to eliminate or override these restrictions, but what they can and must do is refuse to impose them as conditions of use of the program. In this way, the restrictions will not affect activities and people outside the jurisdictions of these governments.
When talking about free software, it is best to avoid using terms like ``give away'' or ``for free'', because those terms imply that the issue is about price, not freedom. Some common terms such as ``piracy'' embody opinions we hope you won't endorse. See Confusing Words and Phrases that are Worth Avoiding for a discussion of these terms.
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Updated: 9 Apr 1999 rms