Calories (mean)
A mean calorie is a unit of energy that was historically used to quantify the amount of energy required to raise the temperature of one gram of water by one degree Celsius, approximately equal to 4.184 joules.
Calories
A calorie is a unit of energy often used in nutrition to quantify the energy content in food. Specifically, one calorie (cal) is defined as the amount of energy required to raise the temperature of one gram of water by one degree Celsius at a pressure of one atmosphere.