A sump pump is a pump that is 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 through the perimeter drains funneling into the pit, or may arrive from natural ground water in the earth. 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.
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. They 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 may be 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 greywater waste from that floor to the lines.
There are generally two types of sump pumps available: pedestal and submersible pumps. 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 as to prevent electrical short circuits.