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From SQL Server Performance]
Auditing is the monitoring and recording all user actions on a database. You can base auditing on individual actions, such as database backup, change of user logins, insert etc. or on combination of factors.
Though auditing has become a popular buzzword, many DBAs and developers still do not appreciate the requirement for auditing
The article continues at
http://www.sql-server-performance.com/articles/audit/2008_audit_intro_p1.aspx