System Log
Important user activity and automated processes such as
subscription expiry checks and the mailer are logged so you can
monitor and check things are running as they should be.
User Logs
In addition to the main system log each user also has their own
activity log which you can view by clicking on the users name and
click the log link. This is useful for example to check what emails
have been sent through the cms to a particular user.
CMS Help - Advanced - System Log