Example: 10 reps at RPE 9, rest 15 seconds, 4 more reps, rest 15 seconds, 3 more. Seventeen hard reps in roughly the time of one set.
It packs effective reps into little time, which suits intermediate hypertrophy work on machines, dumbbells and cables. It is a poor idea under a loaded spine.
Use it on the last set of an exercise and stop the block if the total reps stop climbing.