Answer:
A flashbulb memory.
Explanation:
As the example suggests, a flashbulb memory is a highly vivid, highly detailed memory of a moment. Usually, circumstances are unfrequent and surprising for this type of memory to occur, altough it's not a complete memory. This, then, would explain why many adults can recall where they were and what they were doing the day that Kennedy was assassinated but not an "ordinary", routinary day; given that it was a one in a lifetime experience.
