A "clean install" means removing all existing data and software from a computer or device, and reinstalling the operating system or software from scratch, so that it starts fresh and free of any previous settings or issues. Full definition
Once you have successfully installed this build and activated, you will also be able to clean install on that PC from final media if you want to start over fresh. (techspot.com)
This is with a completely clean install and completely updated. (windowslatest.com)
In addition, some people have reported that it won't fix some system corruption issues, in which case you'd want to perform a real clean install using Option One above. (howtogeek.com)