A fork is a server-side copy of a Git repository under a different user’s GitHub account. Forks enable contributing to projects without write access to the original repository: a contributor forks the project, makes changes on a branch in their fork, and submits a pull request to propose merging those changes upstream. The fork retains a link to the original repository, so GitHub can track the relationship and facilitate pull requests between them. Forks are the standard mechanism for open-source collaboration on GitHub, allowing any user to propose changes to any public project.