Definition
A set structure where weight rises and reps fall across the exercise, or the reverse, instead of every set using the same load.
An ascending pyramid climbs: 12 reps at 60 kg, 10 at 70, 8 at 80, 6 at 90. Reverse pyramid does the opposite, taking the heaviest set first while fresh, then stripping weight: 6 at 90 kg, 8 at 80, 10 at 70.
Reverse pyramid is the stronger option for most clients, because the heaviest set is done unfatigued and therefore heavier. Ascending buys warm-up along the way but the top set arrives tired.
Either way, only the hardest sets are really working sets. Progress the top set first and let the rest follow, or the structure becomes a way of doing many easy sets and calling it a workout.