Auditing is a functionality which keep track of all the activity happening to DB

There are two type of auditing in Oracle

1, Standard Auditing
2. Fine grained Auditing

The standard Auditing is again divided by Statement, Privilege and Object.

Statement - Tracks all action on any type of objects
Privilege - Tracks action on system level
Object - Track action on all the objects (table update, delete etc)

Enabling Audit  Audit_Trail = True in int.ora file

Audit can be of os, db, db & extended etc.

Dba_audit_trail table is data dictionary table gives information on audit.