Categories of SQL statements. DDL (Data Definition Language) defines structure: CREATE, ALTER, DROP. DML (Data Manipulation Language) works with data: SELECT, INSERT, UPDATE, DELETE. DCL (Data Control Language) manages permissions: GRANT, DENY, REVOKE.
In DP-900 you need to recognize the category: adding a column with ALTER TABLE is DDL; changing a price with UPDATE is DML; granting read permission with GRANT is DCL. DELETE removes rows; DROP TABLE removes the whole table.
SQL: DDL, DML, and DCL is a concept that can show up on the exam. Check the full guide to see it in context.