Cleaning units are a term used by some manufacturers to describe the performance of there units. It normally involves a formula which combines the pressure output and the volume output as well as the impact that the spray makes. This is why some manufacturers will list a straight stream nozzle or "turbo nozzle" as having more cleaning performance than a standard fan spray.

True cleaning performance is the combination of pressure, volume and  water temperature as well as spray angle and the distance the nozzle discharge is from the item it is being directed at.