Sump pump
A pump in a basement pit that ejects groundwater before it floods.
A sump pump sits in a pit (the 'sump') at the low point of a basement or crawlspace and pumps out water that collects before it can flood the floor. Test it a couple of times a year by pouring in a bucket of water and confirming it kicks on. If you rely on it, a battery backup pays for itself the first time the power goes out during a storm.