A sump pump is a pump used for drainage that removes accumulated water from a sump pit. A sump pit, commonly found in the home basement, is simply a hole dug in the ground to collect water. The water may enter via perimeter drains funneling into the pit or may arrive from natural groundwater in the earth.
Sump pumps are installed particularly where basement flooding is seen as a problem but are also used to ameliorate dampness by lowering the water table under the foundation. The pipe water away from the house to any place where it no longer presents a hazard, such as a municipal storm drain or dry well. Older properties may have their sump pumps connected to the sanitary sewer, but this is frowned upon now (and maybe against the plumbing code) because it can overwhelm the municipal sewage treatment system. Though in some cases, a sump pump is used when a lower floor is below the sewer lines, to pump grey water waste from that floor to the lines.
Sump pumps are usually hardwired into a home’s electrical system and may have a battery backup. Some even use the home’s pressurized water supply to power the pump, eliminating the need for electricity.
There are generally two types of sump pumps: pedestal and submersible. The pedestal pump’s motor is mounted above the pit, where it is more easily serviced but also more conspicuous. The submersible pump is entirely mounted inside the pit and is specially sealed to prevent electrical short circuits.
Source: Wikipedia