The Free On-line Dictionary of Computing (30 December 2018):

data dictionary
codebook

    A data structure that stores metadata, i.e. data
   about data.  The term "data dictionary" has several uses.

   Most generally it is a set of data descriptions that
   can be shared by several applications.

   Usually it means a table in a database that stores the
   names, field types, length, and other characteristics of
   the fields in the database tables.

   An active data dictionary is automatically updated as changes
   occur in the database.  A passive data dictionary must be
   manually updated.

   In a DBMS, this functionality is performed by the system
   catalog.  The data dictionary is a more general software
   utility used by designers, users, and administrators for
   information resource management.

   The data dictionary may maintain information on system
   hardware, software, documentation, users, and other aspects.

   Data dictionaries are also used to document the database
   design process itself and can accumulate metadata
   ready to feed into the system catalog.

   [Does anybody call them "codebooks"?]

   (2001-04-24)