Depending on the configuration of the software users may see a duplicate icon () next to events on the calendar. The icon will appear only if the logged in user has edit permission on the event. Clicking on the duplicate icon creates a copy of the event with a words 'Copy of' pre-pended to the subject. You may not undo a duplication, simply delete the duplicate if you wish.
To expose this feature you must use an event display string which is described further in the referenced article.
Copy/Paste or Move Events
If there is more than one calendar in the system you will be presented with controls for duplicating the event in a different calendar and/or move the event to a different calendar. When doing so all restrictions on the user are in effect. For example the user may not copy and paste an event into a calendar for which he/she does not have permission or that is locked. If the user chooses the 'move event instead of copy' option the event will be removed from its existing calendar. If this option is not checked the event will be copied not moved.