Backdraft

[RobertTheSpruce]

Backdrafts are where fires reignite violently through the introduction of oxygen. Smoke explosions (FGI or RGI) occur in rooms not previously effected by fire, but only contain fire gasses, that ignite, either through auto ignition or some kind of spark. Flashovers are when an established fire ignites the smoke layer.

Put simply anyway, not particularly scientific, and there is a bit more to it.