Wikimedia Commons has media related to Categories requiring permanent diffusion to zero.

This is a container category. Due to its scope, it should contain only subcategories.

This category contains categories and subcategories of categories tagged with {{Category header|container=yes}}.

Administrative category

This category is part of the administration of Wikipedia and is not part of the encyclopaedia. It contains pages that are not articles or it groups articles by status rather than content.

Tracking category

This category maintains a set of pages tagged with a particular template. Pages are automatically added to the category or one of its subcategories. The category is hidden on its member pages, unless the appropriate user preference is set.

Category category

This category contains categories that are not subcategories.

Container categories are categories intended to be populated entirely by subcategories. {{Container category}}, {{Maintenance category|container=yes}}, and {{Tracking category|container=yes}} will also add a category to this category. See the category pages for possible further details of their contents.