Foreshadowing
The discreet announcement of a future event through clues, echoes or symbols — preparing without revealing.
Foreshadowing sows the early signs of what's coming: a mundane detail, an image, a double-edged line whose reach appears only afterwards. Unlike prolepsis, which shows the future, foreshadowing *suggests* it — the reader should recognize it only on rereading, or in the retrospective shiver of "it was announced."
Well dosed, it produces the feeling of necessity that separates a constructed plot from a sequence of events: the ending feels both surprising and inevitable. Overdone, it becomes telegraphing and kills the surprise. The most reliable calibration tool remains the beta reader: whatever they see coming too early was too visible.
Example
The hairline crack in the dam wall, described in passing in chapter one.