Property:Equivalent URI
From 36C3 Wiki
Property "Equivalent URI" as predefined property contains a "Page" type declaration that is incompatible with the default type of this property.
"Equivalent URI" is a type and predefined property provided by Semantic MediaWiki to represent URI/URL values. This property is pre-deployed (also known as special property) and comes with additional administrative privileges but can be used just like any other user-defined property.
This is a property of type Page.