open source
also: FOSS, free and open source software, FLOSS, free software
Software whose source code is freely available for anyone to view, modify, and distribute under a license that permits these freedoms. Linux itself is open source.
Open source means the underlying program code is publicly accessible, allowing developers to inspect how software works, fix bugs, and add features. This contrasts with proprietary software where only the compiled binary is distributed and the source remains hidden.
Open source projects are typically governed by licenses like the GPL (GNU Public License), MIT License, or Apache License, which define the terms under which code can be used and modified. For example, the Linux kernel is open source under the GPL—anyone can download its source code from kernel.org, study it, patch it for their needs, and contribute improvements back to the community.
The open source model fosters transparency, security (through peer review), and rapid innovation, as thousands of developers worldwide can collaborate on a single project. Most Linux distributions, tools like Git and Apache, and countless utilities rely on this collaborative approach.