Husks are left by some vehicles when they are destroyed, which are burning reminents of the vehicles. They are obstacles to infantry or vehicles, so they can be used to block exits of buildings or single-cell entries in terrain. Blocking the exit of a building delays unit production.
Husks can be destroyed by targeting them with force-fire. If the husk is not destroyed then the fire will stop burning and eventually the husk will disappear automatically.
A mechanic can fix husks at the cost of vanishing.