Flashback

Flashback:  Returning to an earlier time in a narrative for the purpose of making something in the present clearer.

Example:
" When he was nearly thirteen, my brother Jem got his arm badly broken at the elbow."
                          (To Kill A Mokingbird, Nell Harper Lee, pg.2)

This is an example of a flashback because Scout is starting the book by going back to the summer when  her brother broke his arm. This let's us know that she's not that age anymore and that she's going to tell the story in the point of view of her when she was younger.