What is the meaning of Backfire?

To fire in the opposite direction, for example due to an obstruction in the barrel.

To experience a premature ignition of fuel or an ignition of exhaust gases, making a popping sound.

To fail in a manner that brings down further misfortune.

To set a back fire (small, controlled fire to limit spread of a larger fire).

Alternative spelling of back fire

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.

An explosion in the exhaust passages of an internal combustion engine.

An explosion in other equipment.

Source: wiktionary.org