What is the definition or description of: calorie?

A unit of energy: A calorie is the amount of heat energy needed to increase a mililiter of water 1 degree centigrade, the calorie we talk about in foods is really a kilocalorie, that is the amount of energy needed to increase a liter of water 1 degree centigrade... So if you eat a food that is 500 calories that food if burned completely has enough energy to heat a liter of water 500 degrees centigrade.

Nutritional Calorie: The energy needed to raise the temperature of 1 kilogram of water through 1 °c.

Calorie has no Mass!: A calorie is the amount of energy needed to warm a milliliter of water from 3 to 4 degrees centigrade. The calorie unit used for foods is 1, 000 calories, a kilocalorie; the amount of energy needed to warm a liter of water 1 degree centigrade. Calories are the max heat which can be released are measured in a calorimeter, not by eating, are often estimated to ↓cost, have no mass ; thus no weight.