A ration is a fixed allowance of a commodity that is distributed in the event of a shortage. Because war has a tendency to suck up every last item, rationing tends to go hand in hand. Rationing effected both the civilian and military populations. The military got what it needed to fight and the civilians got what was left over.
Japan was the first participant in World War II to institute rationing, with Germany following immediately after its entry and Britain a year later. In all three cases, raw resources such as gasoline were rationed first, being cited as a military necessity. Then food was rationed, with the average civilian getting about 2000 calories a day from bread, milk, and assorted vegetables. In cases of extreme national distress (the Battle of Britain and 1943-1945 for Japan and Germany) manufactured goods had to be rationed, due to the factories being used to create weapons and ammunition.
Rationing was and still is a standard part of military life, with each soldier being guaranteed 2-3 meals a day, a gun, and enough bullets to do his job. Soldiers were issued new uniforms if theirs had become thoroughly worn, new guns if theirs broke, and canned food. This being the hay days of the smoking era, soldiers were also given a cigarette ration of about a pack a week.
A civilian can generally tell how well a war is going by the quality and quantity of their rations. If a civilian gets less, it means the soldiers need more, and that means the enemy is still kicking. Hard. And if a soldier finds his rations reduced, it means his side is in a lot of trouble.
Rationing continued in the Soviet Union because Communism inherently promotes government control.