a unit of heat equal to the amount of heat required to raise the temperature of one kilogram of water by one degree at one atmosphere pressure; used by nutritionists to characterize the energy-producing potential in food
"Nutritionists recommend counting calories to understand how much energy each serving of food provides."
unit of heat defined as the quantity of heat required to raise the temperature of 1 gram of water by 1 degree centigrade at atmospheric pressure
"In physics class, we learned that a calorie is a precise unit of heat representing the energy needed to warm one gram of water by one degree Celsius."
Kilogram calorie or large calorie. A unit of energy 1000 times larger than the gram calorie. It is equivalent to the gram kilocalorie, approximately 4.2 kilojoules.
"In nutrition contexts, when a food label lists an energy value in calories, it actually refers to kilogram calories, which are units of energy roughly four thousand joules each."
In plain English: A calorie is a unit of energy that tells you how much fuel your body gets from food to keep it running.
"I need to eat more calories today because I did some extra exercise at the gym."
Usage: In everyday contexts, "calorie" refers to a small calorie (gram calorie), whereas the scientific definition provided here describes a large calorie or kilocalorie. Always specify "kilocalorie" in formal nutritional science to avoid confusion with the smaller unit used colloquially.
The word calorie comes from the French term calorie, which is derived from the Latin word for heat, calor. Originally used in the early 1800s to describe a specific unit of energy known as the large calorie, the smaller version was defined only decades later.