What is the difference between the master event and an instance in recurring events?
When you add a recurring event to the events calendar, you are entering the master event. Each individual date detailed in that master event becomes an instance of that master event. You may edit either the master event or an instance; however, editing the master event will also change each instance automatically. If you prefer to edit an individual date of a recurring event, you should locate the instance of the event and edit it separately.
