Free software definition

The Free Software Foundation has a specific definition for the term free software. It is embodied in the following article, duplicated from http://www.gnu.org/philosophy/free-sw.html with permission.

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The Free Software Definition

We maintain this free software definition to show clearly what must be
true about a particular software program for it to be considered free
software.

``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.''

Free software is a matter of 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:

    * The freedom to run the program, for any purpose (freedom 0).
    * The freedom to study how the program works, and adapt it to your
      needs (freedom 1). Access to the source code is a precondition for
      this.
    * The freedom to redistribute copies so you can help your neighbor
      (freedom 2).
    * The freedom to improve the program, and release your improvements
      to the public, so that the whole community benefits. (freedom 3).
      Access to the source code is a precondition for this.

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.

The freedom to use a 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 without being required to communicate subsequently with
the developer or any other specific entity.

The freedom to redistribute copies must include binary or executable
forms of the program, as well as source code, for both modified and
unmodified versions. It is ok if there is no way to produce a binary or
executable form, but people must have the freedom to redistribute such
forms should they find a way to make them.


In order for the freedoms to make changes, and to publish improved
versions, to be meaningful, you must have access to the source code of
the program. Therefore, accessibility of source code is a necessary
condition for free 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, without your doing anything to give 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.

Thus, 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,
even to sell copies.

``Free software'' does not mean ``non-commercial''. A free program must
be available for commercial use. Commercial development of free software
is no longer unusual; such programs are free commercial software.

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 publish the program 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. We also have a list
of translations of "free software" into various languages.

Finally, note that criteria such as those stated in this free software
definition require careful thought for their interpretation. To decide
whether a specific software license qualifies as a free software
license, we judge it based on these criteria to determine whether it
fits their spirit as well as the precise words. If a license includes
unconscionable restrictions, we reject it, even if we did not anticipate
the issue in these criteria. Sometimes a license requirement raises an
issue that calls for extensive thought before we can decide if the
requirement is acceptable, including discussions with a lawyer. When we
reach a conclusion, we sometimes update these criteria to make it easier
to see why certain licenses do or don't qualify.

If you are interested in whether a specific license qualifies as a free
software license, see our list of licenses. If the license you are
concerned with is not listed there, you can ask us about it by sending
us email at <licensing@gnu.org>.

Verbatim copying and distribution of this entire article is permitted in
any medium, provided this notice is preserved.

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