Data definition is the process of creating, modifying, or deleting the structure and objects of a database, such as tables, fields, indexes, and views. Data definition is performed using data definition language (DDL), which is a subset of SQL commands. An administrator can use DDL to grant or revoke permissions for a user to access data in a database. References : The Official CompTIA IT Fundamentals (ITF+) Study Guide (FC0-U61), page 144.