Users with taxonomy permissions can make security restrictions on a category-by-category or a "per user group" basis.

By default, the Everyone group, located in the Security tab for each term, has full access to categories. Child categories inherit security settings from parents. If groups have access to content items, the groups can access and apply any taxonomy category to that content item.

Users with permissions may want to limit the groups that can use given taxonomy categories. To do so, configure each category via the Security tab.