data dictionary

A data dictionary, or Metadata Repository, as defined in the IBM Dictionary of Computing, is a "centralized repository of information about data such as meaning, relationships to other data, origin, usage, and format." The term can have one of several closely related meanings pertaining to databases and database management systems (DBMS):

• A document describing a database or collection of databases
• An integral component of a DBMS that is required to determine its structure
• A piece of middleware that extends or supplants the native data dictionary of a DBMS