Creating private WordPress categories
As well as password protecting categories, the Password Protected Categories plugin lets you mark categories as private. This works in exactly the same way as private WordPress pages or posts, which you can read about in the WordPress Codex.
Who can see private categories and their posts?
For most sites, only logged in Editors and Administrators can see private categories and the posts within them. You can change this by editing the permission levels for your site.
How to create private categories in WordPress
To mark a category as private, go to the Add or Edit Category screen for your post type (e.g. Posts -> Categories) and click the option to either add a new category or edit an existing one.
In the ‘Visibility’ section above the ‘Add New Category’ button, select ‘Private’ before saving your category.
You can have as many private categories as you like, while leaving the remaining categories public.