Software fork

A fork of a free software project--or free content project--is a version of the original software that makes use of the same (or a compatible) open source license, but which is itself incompatible with the original version.

A fork can also exist within a project, when code is divided into branches. For instance, Firefox development occurs on multiple codebases at the same time. While development on Firefox 2.0 was ongoing, other developers were working on 3.0, while patches and support continued to be issued for version 1.5. Other projects have "stable" and "development" branches, where code from the unstable branch is moved to the stable branch when it is thoroughly tested.