Hope brothers here can help me clarify:

I don't really understand difference between submersible pump and power head.
My understanding is: submersible pump hv to be submerged in water whereas power head can be placed above/outside tank (eg place with overhead filter box). Am I correct or totally wrong? Please advise.

I am confused because certain filter like Dolphin 808: the box states power head top filter, but instructions say must be submerged in water.

Then Super Boy filter states "Submersible Pump & Power Head" on the box. Does that mean that I can place the pump above water?

Please enlighten, cheers...