Sump pumps normally work in combination with a sump pit.
The sump pit is simply a hole dug into the ground generally
in the basement or crawlspace of a house, which allows water
to collect in it. The pump then pumps the water out of that
sump pit hole.
A basement or crawlspace sump pump is most often used in
situations where the house's basement or crawlspace is below
the water table level or where flooding is common. But those
are not the only areas where a sump pump and pit may be
deemed useful. In most homes that have a basement, odds are
they have a sump pump, especially if they have a finished
basement with furniture in it.
There's usually two types of sump pumps: a pedestal, or
upright style and a submersible style. As their name
reflects, the pedestal style sump pump sits above the sump
pit, and it's easier to reach and perform maintenance and
cleaning. A submersible sump pump actually goes down into
the sump pit itself. The submersible sump pumps are
difficult to reach and perform maintenance on of course, but
they are sealed in a sealed housing to prevent electrical
short circuits when water collects in the pit.