The original event is something that happens at a particular place at a particular time.  What is stored in memory depends not only on the original event but also on other factors such as the cognitive state of the individual at the time of the event.   A car accident that happens at a particular intersection at a specific time would be an example of an original event.   The memory that is stored would also include the emotional and physiological state of the observer (i.e., the cognitive environment).