Use
You can cancel both internal and external business events in both planned and firmly booked status. When you cancel a business event, the system appends the relevant flag to it.
Features

You specify whichever of these two options you wish to use in Customizing for Training and Event Management under Recurring Activities ® Firmly Book/Cancel ® Control Data in the SEMIN FIXRV entry.
When you firmly book a business event, you can also specify what the system response should be in a specific case, thus overriding the Customizing settings. You do so by choosing Settings ® Procedure Waiting List. This does not change the standard settings in Customizing.
Results

Cancellation of a business event is final and irrevocable. Once a business event has been canceled, it cannot ever be held. Thus, if you simply want to remove a business event temporarily from the business event catalog, you should use the Lock function.
See also:
Lock Business EventsCanceling a Business Event