noun, plural: calories
(1) Gram calorie: unit of heat energy that is equal to the amount of heat needed to raise the temperature of 1 gram of water by 1 degree Centigrade at 1 atmospheric pressure.
(2) Kilocalorie: a measure of heat energy that is equal to the amount of heat needed to raise the temperature of one kilogram of water by one degree Centigrade at one atmospheric pressure.
Calories are used to describe the energy-producing potential of food. A one gram calorie is equal to 4.1840 joules. Joule (which is an SI unit) is now more preferred over calorie (which is nonSI unit) for measuring heat energy.
Word origin: from Latin calor, heat
Abbreviation: cal (gram calorie) or kcal (kilocalorie)