A sump pump is a pump that is installed in a sump pit in some basements. Usually this sump pit is connected to perforated piping that goes all around the house underground. Water enters these pipes through the perforations and flows into a pit. The sump pump sits in this pit and when it fills with water the pump comes on to pump the water away from the home. The alternative would be water building up underground around your home and possibly leaking in to the basement through the foundation. This systems is very effective at collecting water and pumping it away into the storm drain rather than winding up in your basement.