Definition of friendly fire

a fire kindled intentionally to serve a useful purpose and contained in a receptacle such as a fireplace or stove; any damage it may do is not covered by fire insurance. A military use of the term means being shot at by your own troops.

kindling intentionally set in a fireplace, stove, furnace, or other containment that has not spread beyond it. Property insurance does not protect against damage from a friendly fire. For example, smoke damage to the inside of a fireplace is not covered because the fire is in its normal habitat; to insure it would be insuring against a certainty. Insurance is designed to provide coverage against the fortuitous loss.