1 [C,U] a part of a film/movie, play, etc. that shows a scene that happened earlier in time than the main story:
The events that led up to the murder were shown in a series of flashbacks. * The reader is told the story in flashback.
2 [C] a sudden, very clear, strong memory of sth that happened in the past that is so real you feel that you are living through the experience again:
war veterans suffering from nightmares and flashbacks
