Well, the term calorie is used loosely to describe energy, but there are two types of calories. There is a small calorie, that is used to describe small energy increments per gram of substance, which is a small mass. It takes 1000 of these small calories to make one large calorie, which is the one we use to describe the energy contained in food. The calorie used in a large calorie is typically capitalized with a large "C" to distinguish it from the smaller unit calorie. So "Calories per serving" on the nutritional label of most manufactured foodstuffs in grocery stores today is an indication of how many energy units per serving that food contains. It is a unit based on the SI (metric system) already, and while being somewhat outdated in terms of energy units outside of food content, is still recognized as the gold standard in terms of recognition among persons who include "Calorie count" as part of their daily dietary regimen.
I think it was Kcal