SQL can be divided into following 2 parts.
- DML – Data Manipulation Language
- DDL – Data Definition Language
DML part consists of query and update commands like SELECT, UPDATE, DELETE, INSERT etc. ABAP programs handle DML part of SQL.
DDL part consist of commands like CREATE TABLE, ALTER TABLE, DROP TABLE, CREATE INDEX etc. ABAP Dictionary handles DDL part of SQL.
So ABAP Dictionary is used to create and manage data definitions (metadata). ABAP Dictionary is used to create Tables, Data Elements, Domains, Views, Lock Objects etc.