How does hidden category work?

A hidden category is an dynamic product collections to be used in for eg. campaigns or CMS widgets

Hidden category makes it possible to have a category active on the site without it being shown in the menu or in filter. A hidden category can still be reached via an URL and indexed and searchable on google if on sitemap.

This makes it possible to have categories that are popular searches on google without it needing to be in menus and filtering.