Subscriber, editor, author and contributor are built-in WordPress user roles. In case you have already created new user roles using popular User Role Editor or any other plugin and now you don’t need default WordPress user roles on your website. You can easily remove them by creating a new PHP function.
The tutorial is on adding a new Webmaster user role which comes in between your site Administrator and Editor. This user is same as site Administrator but it excludes some capabilities like managing plugins, changing themes. Users with this role will not be able to install or activate any theme or plugin. They can change the widgets, edit theme options like background, header images etc if your theme provides and do all other things which a site admin does.