1. Insurance.a fire deliberately set and remaining contained, as in a fireplace or boiler, from which any resulting loss cannot be claimed as an insurance liability (opposed to hostile fire).
2. (in military combat) fire, as by artillery, by one's own forces, esp. when causing damage near or casualties to one's own troops.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.