According to official US Department of Defense and NATO definitions, a front can be "the line of contact of two opposing forces.
[1] Conversely, the term "home front" has been used to denote conditions in the civilian sector of a country at war, including those involved in the production of matériel.
Front can also refer to the lateral space occupied by a military unit as measured from the extremity of one flank to the other.
For example, under the military doctrine of the Soviet Army and those which copied it, the amount front occupied by an attacking unit depended on its size.
The term "front line city" was used by the Germans during their long retreat from Moscow/Stalingrad to refer to metropolitan centres that had become disputed by the two combatants.