I sump is Aquarium or box below your aquarium that receives water from your display thru an overflow. In the sump you will place the equipment that would have been in your aquarium. Such as a protein skimmer heater containers that hold carbon or other water filtering materials. The water is then pumped back up into the aquarium.
What you posted was a sponge filter. Which is used I grow bacteria to process ammonia. It is placed in the aquarium. One could place it in the sump but is more often seen in the aquarium itself.