The software deals with five basic types of data. These are:

Calendars
Contacts
Events
Dropdowns
Users
User Groups

Each of these items behaves similarly when deleted. When one deletes an item from a database that item is not physically removed. Instead, the item is simply marked as having been deleted. For all subsequent operations the item is ignored. In this way, the system gains a powerful, unique feature: undelete. Whenever you delete a calendar, event, user or user group you will be able to undelete that item. Deleted items are not physically removed from the database until they are compacted or cleaned.

Cleaning the database spins through each record and completely removes those items that were previously deleted. Cleaning is an non-recoverable operation. After removal you may no longer access these items. For this reason you may wish to make an archive of the calendar before proceeding with a cleaning.