Lets say someone asked you what are the Oracle database built-in accounts (Oracle internal) in your current database ?

Most oracle database dictionary views have a column called ORACLE_MAINTAINED that was introduced in Oracle 12c release.

https://docs.oracle.com/database/121/REFRN/GUID-309FCCB2-2E8D-4371-9FC5-7F3B10E2A8C0.htm#REFRN23302

 

SQL> select username,last_login,oracle_maintained from dba_users where oracle_maintained=’Y’;

Finding Oracle built-in roles:

 

SQL> select role,oracle_maintained from dba_roles where oracle_maintained=’Y’;