GlossaryCraft technique
Flashback
Also: END FLASHBACK · flash forward
A flashback is a scene from the past dropped into the present story. It shows the audience something that already happened, like a memory or a secret. Mark it clearly so the reader always knows when they are.
The simplest way to write one is to add FLASHBACK to the scene heading, then END FLASHBACK (or BACK TO PRESENT) when you return. For a longer stretch in the past, some writers use a SUPER with the year instead.
A flashback should give the audience something they need right now, at this point in the story. If it only repeats what we could guess, cut it. A scene from the future is a flash forward.
INT. SAM'S CAR - NIGHT Sam stares at the old house. FLASHBACK - EXT. SAME HOUSE - DAY (1999) Young Sam runs across the lawn, laughing. END FLASHBACK