The literal translation is "by fire and sword." It is used to describe a destructive terrorist raid with the intent to drive out a population. It can be written several different ways. For example: "igni ferroque," "ferro ignique," "ferro atque igni," "ferro atque flamma," etc.
Examples from the Oxford Latin Dictionary (thanks to Hamish Carr for finding them):
Livy, 10.12.8:
Omnia ferro ignique vastantur; praedae undique actae.
Everything was devastated by sword and fire; loot was gathered from everywhere.
Livy, 35.21.10:
Minucius nihil deinde laxamenti hostibus dedit; ex agro Pisano in Ligures profectus castella vicosque eorum igni ferroque pervastavit.
Minucius then gave the foe no time to relax: he set forth from the Pisan country to the Ligurians and devastated their strongholds and villages with fire and sword.
Livy, 38.6.4:
Ferro ignique gesta res; . . .
The fight continued with sword and fire; . . .
Tacitus, Annals 14.38 (Referring to the Rebellion by Boudicca)
Cohortes alaeque novis hibernaculis locatae, quodque nationum ambiguum aut adversum fuerat, igni atque ferro vastatum.
The allied troops were put into winter quarters, and those tribes which had been fence-sitting or fighting against us, were harried with fire and the sword.
Cicero, Philippics, 13.21.47:
Sanctiore erunt, credo, iure legati quam duo consules, contra quos arme fert, quam Caesar cuius patris flamen est, quam consul designatus, quem oppugnat, quam Mutina, quam obsidet, quam patria, cui igni ferroque minitatur.
I hope that envoys will be safer (with him) than the two consuls, against whom he rose up in arms; safer than Caesar, who was his father's priest; safer than the consul-elect, whom he attacked; safer than Mutina, which he besieged; safer than his own homeland, which he attacks with fire and with sword. | 
