Free software

Software that grants users the freedom to run it for any purpose, study and change its source code, and share copies or modified versions.

Free Software Foundation: A nonprofit organization founded in 1985 to promote computer users’ freedom and support free software. It defines and advocates the freedoms at the center of this concept.
Richard Stallman: An American programmer who launched the GNU Project and founded the Free Software Foundation. His work gave the movement its name, institutions, and early legal strategy.
Open-source software: Software distributed with source code under terms allowing use, modification, and redistribution. It often describes the same software, but emphasizes practical development benefits rather than ethical freedom.
Linux kernel: The kernel of the Linux operating system, distributed under version 2 of the GNU General Public License. Its license allows modification and redistribution while requiring distributed derivatives to preserve its terms.
GNU/Linux: An operating system combining the Linux kernel with GNU tools and other software. It is a major result of combining the GNU Project with the Linux kernel.
GNU General Public License: A family of licenses that grants software freedoms and requires shared derivative works to preserve them. Its copyleft terms are a prominent way to protect users’ freedoms.
GNU Project: A project begun in 1983 to develop a Unix-like operating system composed entirely of free software. It turned the movement’s principles into an ambitious software-building effort.
Proprietary software: Software whose license restricts users’ ability to study, modify, or redistribute it. Its restrictions deny freedoms that define free software.
Debian: A community-developed operating-system distribution composed primarily of free software. Its Social Contract and Free Software Guidelines make freedom a distribution policy.
Copyleft licensing: The use of copyright licenses to require shared modified works to preserve specified freedoms. It made freedom a condition of redistribution across many software projects.

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