A database containing data about all the databases in a database system. Data dictionaries store all the various schema and file specifications and their locations. They also contain information about which programs use which data and which users are interested in which reports.
In computing, a file that holds data about data—for example, lists of files, number of records in each file, and types of fields. Data dictionaries are used by database software to enable access to the data; they are not normally accessible to the user.