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.
Calories (thermoc.)
A thermochemical calorie (cal_th) is defined as exactly 4.184 joules. It is roughly the energy needed to warm one gram of water by one degree Celsius.