What's a hollow nozzle

Hi, i found this but would like to know how and what's the hollow nozzle.

Thanks

Water obviously can't pass through a nozzle that's not hollow to some degree. You don't want it too thin. Won't increase the flow. It's the width of the opening where the bag and the hose meet, and the height that controls the rate of flow.

Before I would answer that one, I would like to see the context/reference first...