Pacing
Also said as Rhythm of play, Beats
The order and length of what you ask of the player: fight, rest, explore, talk, fight again. It is about what comes after what, more than how hard any one part is.
Non-stop action wears people out and makes each fight feel the same. Long quiet stretches lose them. A strong moment gets its strength from what came just before it.
Say it
“After each boss, give the player a safe room with a save point and no enemies for at least a minute. Then one short fight to warm up, and only then the next big setpiece.”
Where you’ve seen it
Doom (2016) alternates sealed arena fights with quieter corridors of exploring and pick-ups, so each new arena lands as an event.
Not to be confused with difficulty curve
A difficulty curve is how hard things are. Pacing is what you do, and when. An easy game can be badly paced, and a hard one beautifully.