To stop an advancing fire by setting in front of it, or around threatened buildings, woods, etc., another fire, which is then beaten out, thus producing a protective burnt area.To light before the proper time: said specifically of a gas-engine when the charge explodes before the admission-valve closes, thus making an explosion in the admission-passage, or before the working-piston reaches its dead-center, which it must do before beginning its working stroke. See back-firing.n. A fire started purposely some distance ahead of a fire which is to be fought.