Free software is computer software that is distributed along with its source code, and is released under terms that guarantee users the freedom to study, adapt/modify, and distribute the software. Free software is often developed cooperatively by volunteer computer programmers as part of an open-source software development project.
Free software differs from proprietary software (such as Microsoft Windows), which to varying degrees does not give the user freedoms to study, modify and share the software, and threatens users with legal penalties if they do not conform to the terms of restrictive software licenses. Proprietary software is usually sold as a binary executable program without access to the source code, which prevents users from modifying and patching it, and results in the user becoming dependent on software companies (vendor lock-in) to provide updates and support. Free software is also distinct from freeware, which does not require payment for use, but includes software where the authors or copyright holders of freeware have retained all of the rights to the software, so that it is not necessarily permissible to reverse engineer, modify, or redistribute freeware. Thus, free software is primarily a matter of liberty, not price: users are free to do whatever they want with it – this includes the freedom to redistribute the software free-of-charge, or to sell it (or related services such as support or warranty) for profit.