A powerhead is a submerged water pump. Though the functions are essentially similar, it does have a few features that a normal water pump does not have. For starters, it can accept air from the surface. This is done with the help of a hose that goes directly to the surface. This process of aeration gives superior air quality. At other times, the Powerheads can be used to pump water. The numerous technological advances in the sphere of powerheads have meant that they now possess various features that give increased functionality. Some of the powerheads in use today, come with a filter that is built-in, and which significantly increases water clarity.

Source: https://www.outboardclinic.com/remanufactured-powerheads/