- A premature explosion in the cylinder of a gas or oil engine during the exhaust or the compression stroke, tending to drive the piston in the wrong direction.
- (firefighting) Alternative spelling of back fire
- An explosion in the exhaust passages of an internal combustion engine.
- To fail in a manner that brings down further misfortune.
"His attempt to make money by importing luxury cars backfired horribly when fuel prices tripled."
- (of a gun, cannon, Bunsen burner, etc.) To fire in the opposite direction, for example due to an obstruction in the barrel.