Definition
A fork is an independent copy of an existing project or repository, created so it can be modified and evolved on its own. On hosting platforms like GitHub, forking specifically means making a personal copy of a repository you do not have write access to.
How it works
When you fork a repository, the platform copies it, along with its commit history, into your own account, and the two copies then evolve independently. To get your changes back into the original project, you typically open a pull request from your fork, which the maintainers review and merge.
Usage
Typical uses include contributing to open source projects, deriving your own version from an existing one, and experimenting with uncertain changes without touching the original repository. The word also describes larger splits in open source, where a community branches off into a new derivative project over disagreements about direction or governance.
Related and confusable terms
A forked project inherits the original project’s license obligations, which is why fork and GPL are often discussed together: the GPL requires derivative works to be distributed under the same license.