Ejector pumps: are used to lift sewage that is below the city sewage system to that level. For disposal, typical uses for this are basement homes or homes built below street level. They typically have a storage tank and an alarm flashing light to alert you of a malfunction. Cities also use these systems on a larger scale to move sewage up and over hills.
Sump Pumps: While in the same family are typically used to move rain water from areas that it may collect below any gravity drainage area up to a safe disposal site. They may pump to the outside or may be connected to the plumbing system. Pool pump is one of sump pumps.