This would be coverage for your basement, when water gets in from a sump pump failure, pipe break or sewer backing up (like a clogged sewer line). Many insurance companies give you $2,500 for this or some $0 coverage – it must be added on as an endorsement. Then you can also buy more coverage, like $10,000, $20,000, $30,000 for finished basements. Some insurance companies do have a maximum limit they will go to, so you need to check with yours.
This is a great endorsement to have added on, even in an unfinished basement. You have your furnace or boiler down their, maybe a dehumidifier too. Washers/Dryers, hot water tanks, all can be affected by water backing up.