http://www.gnu.org/philosophy/free-sw.html

"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...

See also OpenSource for related links - OpenSource is similar but not identical to FreeSoftware.