Noun

1. The backward escape of gases and unburned gunpowder after a gun is fired
2. A loud noise made by the explosion of fuel in the manifold or exhaust of an internal combustion engine
3. A fire that is set intentionally in order to slow an approaching forest fire or grassfire by clearing a burned area in its path
4. A miscalculation that recoils on its maker

Verb

1. Come back to the originator of an action with an undesired effect
2. Emit a loud noise as a result of undergoing a backfire
3. Set a controlled fire to halt an advancing forest to prairie fire