An user account is not a physical structure in Database but it is having important relationship to the objects in the database and will be having certain privileges.
Privilege auditing is the auditing of the use of powerful system privileges without regard to specifically named objects.
Each database user is assigned a Profile that specifies limitations on various system resources available to the user.
Auditing includes reading, writing and deleting the access on the objects at the table level. The privileges granted to a user can be audited
There are three levels of auditing
Each server and background process can write an associated trace file. When an internal error is detected by a process or user process, it dumps information about the error to its trace. This can be used for tuning the database.