When you create an external table of a particular type, you can specify access parameters to modify the default behavior of the access driver. Each access driver has its own syntax for access parameters. Oracle provides two access drivers for use with external tables: ORACLE_LOADER and ORACLE_DATAPUMP.
These access parameters are collectively referred to as the opaque_format_spec in the SQL CREATE TABLE...ORGANIZATION EXTERNAL statement.
Oracle Database SQL Language Reference for information about specifying opaque_format_spec when using the SQL CREATE TABLE statement