Pacing
Managing a story's speed: alternating scene and summary, accelerations, slow-downs, breathing room.
Pacing is the story's perceived speed and the art of varying it. Its basic mechanics oppose scene (narrative time matches story time: dialogue, live action) and summary (the narrative compresses: "winter passed"). More locally, sentence and paragraph length set the tempo — short sentences for urgency, ample periods for contemplation.
The classic error isn't slowness but uniformity: an all-action narrative exhausts as much as an all-contemplation one, because without variation there's neither relief nor anticipation. Pacing is hard to diagnose from inside — it's one of the things reading aloud and beta readers reveal most reliably.
Example
Three pages for a one-minute duel; one sentence for the ten years after.