Calories (nutritional)
A nutritional calorie, specifically a kilocalorie (kcal), is the amount of energy required to raise the temperature of one kilogram of water by one degree Celsius. In nutritional contexts, the term "calorie" typically refers to a kilocalorie.
Calories (15°C,CIPM, 1950)
The calorie defined as CIPM, 1950 or the "15°C calorie" is a unit of energy that was historically used to quantify the amount of heat required to raise the temperature of one gram of water by one degree Celsius at 15°C. This definition was established by the International Committee for Weights and Measures (CIPM) in 1950.