A flashbulb memory is a memory of an event that had an important emotional impact on a person. The memory is not completely accurate as to details, but it lasts for a very long time without decaying. The memory is long lasting because of the emotion connected to it.
You might hear people talking about how well they remember exactly where they were and what they were doing when they heard a particular piece of news. In my parents' generation, one such event was the assassination of John F. Kennedy. The emotion evoked by the news triggered a flashbulb memory in many people.
Flash bulb memory refers to a recollection of events around the time when people are witness to something that involves them emotionally in a strong way. Examples of these could be something that has a lot of consequence for the person or which is very surprising, shocking or disturbing in nature.
During these events people are able to vividly recall where it occurred, what was happening when they heard or saw it, who told them about it, how they and others around them reacted and what happened subsequently.
Flashbulb memories are very deep and are usually not forgotten even after a long duration of time.