A "flashback sequence" is when a story or movie goes back in time to show something that happened earlier. It is like remembering something from the past while you are in the present. Full definition
Monroe will appear in flashback sequences with Lipinski (who plays the young version of Brolin's convict and bears a frightening resemblance to him) as Mandy, a farm girl romanced by Brolin / Lipinski before he left for Vietnam, who will later become his wife and the mother of his child. (indiewire.com)
I am hoping for flashback sequences of baby Cesar, although great action will do just fine. (iheartthetalkies.com)
Bottom line apart from extra fight bits and various other odd small scenes the main crux of the director's cut are a few flashback sequences where Riddick sees a spirit - like entity of one of his people. (rottentomatoes.com)