The bilge is the lowest part of the inside of the hull, where any water aboard ends up. The bilge pump takes it out. Most boats have an electric pump started by a float switch, and a manual pump as a backup.
The number on the box is optimistic. Good Old Boat says pumps are rated at zero head, and that the lift and the hose bring one down to about 40 percent of its rating. Practical Sailor recommends 1,000 to 1,500 GPH for the primary on a 30 to 35 ft boat, with about 2,000 GPH for a backup mounted higher.
What a surveyor checks
The automatic pump started the way a leak would start it: water poured into the bilge to lift the switch, rather than a hand on the float. That it discharges overboard and stops again. The switch for debris and corrosion. A second pump and a high-water alarm, which ABYC H-22 asks for on boats with enclosed accommodation. The discharge, which needs to sit high enough not to siphon back or have a vented loop and a seacock. Then how often the pump runs, because a pump that cycles all day is telling you about a leak.
In the report
"Main bilge pump float switch jammed with debris, pump did not start when the bilge was flooded. Clean or replace the switch before the vessel is left afloat unattended." See bilge pump float switch failure.