Generator — Generators compute a value for the account attribute, usually based on a pattern you specify. Select the name of a generator that will create the value for the source attribute during provisioning. For example, the Create Unique Account ID generator produces an account ID for each account based on the pattern you enter in the Pattern Used field.
This is the companion discussion topic for the documentation at https://documentation.sailpoint.com/connectors/active_directory/help/integrating_active_directory/updating_account_creation.html