The information that describes another set of data (ie data about data). It is used to establish a common naming terminology and/or a common repository for instances of the same data. Applicable mainly to IDM attributes, data warehousing cubes and data exchange events. For example; surname, last name, family name, employee name, customer name, staff-surname may all be described as "SN" in an IDM repository or in XML.

Source: http://identityaccessman.blogspot.com/2006/08/identity-dictionary.html