Cluster sets are the intensity booster your strength workout.
Cluster training occurs when you incorporate short rest periods into a set to relieve fatigue and produce greater power.
Cluster training allows you to maintain power, force and good form for every rep lifted.
For example, in a set of 5 reps, you can take a short rest in between reps (10-30s). So you will do a total of 5 reps like a 1+1+1+1+1.