Help:Namespace prefix

Subjects that are distinguished by a namespace prefix (separated with a colon ) represent the broadest level of classification that the MediaWiki software has build-in support.

Query usage
According to Magic words (Page names),  contains the "Full page title (including all subpage levels) without the namespace" where   is to hold the "Namespace and full page title (including all subpage levels)".

For example, a subject  with a query containing either   or   will differ in its results:
 * where  creates a reference to
 * with  is expected to create a reference to