SIt is an aquarium internal filter/pump, specifically SOBO FD-1501.
It is used inside a fish tank to:
Filter dirty water — the sponge/filter material catches dirt and waste.
Circulate the water — keeps water moving.
Oxygenate the water — the water movement helps increase oxygen.
It can be used for freshwater and saltwater aquariums.
The box says 15 W and up to about 800–1000 L/hour flow.
So basically, you put it inside the aquarium, completely submerged, and it continuously pulls water through the filter and returns cleaner water