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

Data definition language

    (DDL)

   1. A language enabling the structure and instances of a
   database to be defined in a human-, and machine-readable
   form.

   SQL contains DDL commands that can be used either
   interactively, or within programming language source code,
   to define databases and their components, e.g. CREATE and
   DROP.

   See also Data manipulation language (DML).

   2. A specification language for databases, based on the
   entity-relationship model.  It is used in the Eli
   compiler-compiler to manage type definitions.

   ["DDL Reference Manual", ECE Dept U Colorado, 1991].

   (1999-04-26)