A fork classically means the further development of open source software. Since open source software is naturally freely accessible and can be downloaded by anyone, everyone has the opportunity to make their own copy of the software and modify it for their own purposes. This would have forced the person to make the software.
The modification of the software should not be seen as an evil intervention, but even as an elementary and desirable part of open source projects. Users with programming knowledge can thus add new functionalities according to their own needs — so different distributions of software can exist.