The technique of a story skipping around in time, including flashbacks and flash-forwards, is often referred to as non-linear narrative or non-linear storytelling. In this structure, the narrative is not presented in chronological order, allowing the author to explore different time periods in a character's life, reveal backstory, or foreshadow future events.
Flashbacks typically provide context or background that enhances the understanding of characters and their motivations, while flash-forwards may create suspense or hint at future developments in the plot. This storytelling approach can deepen emotional impact and enrich the narrative by providing a more complex view of the characters and events.