Namespaces are an alternate way defined by MediaWiki to organize pages instead of using categories. When a page is linked, all of the title must be filled in - this includes the Namespace.
 MediaWiki Namespaces
Special Pages are pages that are created by MediaWiki itself. Other Special pages cannot be created by anyone that is not an administrator on NeoWiki - they cannot be edited, but certain properties can be changed depending on the page itself (ex. Create Page).
This is a Namespace that rarely appears. Instead, it is hidden, and shows the Content pages on a Wiki. All pages that don't have a visible Namespace will have this by default.