Open source

Open source is a software development and distribution model whose licenses permit users to inspect, use, modify, and redistribute source code.

Open-source license: A legal license granting permissions to use, modify, and redistribute software whose source code is available. Its terms establish which uses and redistributions an open-source project permits.
Richard Stallman: An American programmer and activist who founded the GNU Project and the Free Software Foundation. His GNU work helped establish a durable model for freely shared software.
Free software: Software distributed with users' freedoms to run, study, modify, and share it. It shares core permissions with open source but frames them as user freedoms.
Linux: A family of operating systems built around the Linux kernel, distributed in many forms under open-source licenses. Its kernel and distributions demonstrate open source at global infrastructure scale.
Linux kernel: The core of the Linux operating system, developed by a large distributed community under the GNU General Public License. Its development illustrates how many organizations can coordinate around a shared codebase.
GNU General Public License: A family of copyleft software licenses that requires redistributed derivative works to remain under the same license. Its reciprocal terms exemplify how open-source licenses can preserve downstream freedoms.
GNU Project: A project launched in 1983 to develop a Unix-compatible operating system composed of free software. It supplied foundational software and licensing ideas later central to open-source development.
Proprietary software: Software whose owner restricts access to source code or limits use, modification, or redistribution through licensing. Its restrictions mark the opposite distribution model.
Apache HTTP Server: An open-source web server maintained by the Apache Software Foundation. Its widespread deployment shows how openly developed software serves the public web.
Heartbleed: A 2014 vulnerability in OpenSSL that allowed attackers to read sensitive memory from affected systems. It exposed the security risks of relying on critical open-source projects with limited maintenance resources.

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Free-culture movementCompared with: Its pragmatic framing differs from free culture’s explicit emphasis on freedom.