Metadata – Tag pages
The menu items Tags (first: Abc) is an option that is activated as a default. This feature offers an alternative way to gather information: by subject rather than filed in folders. All (Predefined) Tags have been collected on this page. For each (Predefined) Tag, a Definition page is available that displays all information linked to this (Predefined) Tag.
If you visit a group, this page only shows the (predefined) tags used in this group. The menu item Tags on the Homepage is collective and shows all items of the domain. The displayed information depends on the members permissions level: a member will only see those items for which he has at least reading permission.
The name already says it: the definition page allows you to give a definition to the (predefined) tag. Since all members can contribute to the definition, this will create a common reference framework.
Various options of the menu item Tags can be disabled via Setup > Metadata > Tag pages.