This is an XML namespace defined in the "Composite Capability/Preference Profiles (CC/PP): Structure", and "CC/PP Attribute Vocabularies". The latest version can be found at http://www.w3.org/TR/CCPP-struct/, and http://www.w3.org/TR/CCPP-vocab/.
For more information about CC/PP, please refer to the W3C CC/PP Working Group page. For more information about XML, please refer to The Extensible Markup Language (XML) 1.0 specification. For more information about XML namespaces, please refer to the Namespaces in XML specification.