Free software
The word "free," in the term "free software," refers to liberty rather than to pricing. To say that a piece of software is free means that anyone who has a copy of it
- may run it, for any purpose;
- may study it and modify it, to make it do what he or she wants it to;
- may share copies of it with anyone; and
- may give copies of his or her modified versions to anyone.
Exercising some of these freedoms requires access to the source code for the software, so the source code for free software is always distributed, or at least made available, along with the executable program. However, access to source code is not sufficient to make a piece of software free. The best way to ensure that the software that you create is free and remains free is to publish it under the GNU General Public License. This license not only establishes the freedoms listed above but uses copyright law to ensure that people who copy, share, or adapt your software cannot impose more restrictive licenses either on your software or on their own derivative works.
Free software is defined more fully in the free software definition provided by the Free Software Foundation, which also maintains a list of frequently asked questions. The Software Freedom Law Center provides legal services to developers of free software.