Some of the possible variations are described below. Free software is a matter of freedom, not price. This has nothing to do with what we mean by free software in the GNU project. Because of this potential confusion, when a software company says its product is free software, always check the actual distribution terms to see whether users really have all the freedoms that free software implies. This is unfortunate, because such a word would be useful here.
Free software is often more reliable than non-free software.
Public domain software Public domain software is software that is not copyrighted. It is a special case of non-copylefted free software , which means that some copies or modified versions may not be free at all. Copylefted software Copylefted software is free software whose distribution terms do not let redistributors add any additional restrictions when they redistribute or modify the software. This means that every copy of the software, even if it has been modified, must be free software. See Copylefted for more explanation of how copyleft works and why we use it.