A calorie is a unit of energy. In nutrition and everyday language, calories refer to energy consumption through eating and drinking and energy usage through physical activity. For example, an apple may have 80 calories, while a 1 mile walk may use up about 100 calories.
There are two types of calories:
- A small calorie (symbol: cal) – 1 Cal is the amount of energy required to raise one gram of water by one degree Celsius.
- A large calorie (symbol: Cal, kcal) – 1 Cal is the amount of energy required to raise one kilogram of water by one degree Celsius.
1 large calorie (1 kcal) = 1,000 small calories.
Source: MedicalNewsToday, http://www.medicalnewstoday.com/articles/263028.php