Flak guns are warship-mounted anti-fighter point-defense weapons, designed and put into service sometime during the Reconstruction period. Oddly enough, the Shivans also seem to have adopted this technology at some point prior to their reappearance in the Second Shivan Incursion.
Flak is generally more effective against fighters and bombers than warships. However, flak guns are also effective against other smaller-sized ships such as transports, freighters, and even weaker cruisers. When a projectile of flak explodes, it has a small damage radius. Flak projectiles usually do more damage on hull plating than on shields. Flak guns are also known to be nearly useless against subsystems. Counter-intuitively, flak guns are less useful at intercepting warheads in-flight than standard blob turrets due to an increased shot spread.