What are perils?
Perils are events that cause damage or loss to your property. Under an HO-3 policy, you are covered for everything except for things that are specifically listed as perils that policy won't cover. This is called an "open perils" basis of coverage. There are also "named perils" (usually like fire, theft, etc.) that it will cover you against.
Basically, your insurance company will pay to repair or replace your damaged property as long as it is listed as a "named peril" or it's a peril that is not excluded in writing.