Let's start with flood insurance. Flood insurance is , as the name implies, a type of insurance that covers you in the event of a flood as defined by your federal government. A flood, according to most federal governments, is when two properties or two or more acres have been effected by a flood. Alongside that, the federal government has to declare said area has been impacted by a flood.
Flood insurance is not included in your homeowner's insurance policy. Flood damage is not typically covered by your homeowner's insurance policy either. If you live in an area participating in the National Flood Insurance Program, you're eligible to purchase a flood insurance policy separately.
Water backup coverage is something not to be associated with your homeowner's insurance nor flood insurance. Water backup coverage is a policy that can be obtained in addition to your homeowner's insurance, usually for a low price. It provides coverage in the event that water backs up and comes up through pipes, drains, sewers or some pump failure to name a few examples. You're generally covered if the water came back up into your home or business. The cleanup and anything required to fix the problem tends to be covered by your water backup coverage.
If you went on vacation and came home to find that your sump pump failed and there's 5 inches of water in your basement, then this is something that can be covered by your insurance through your water backup coverage.