Calories are a measure of energy. It refers to the amount of energy you eat and drink or the amount of energy you burn when exercising.
Energy can also be measured in kilojoules (kcal) and kilojoules (kJ) depending on where you live.
This can cause you to feel overwhelmed, especially if you are counting calories or comparing the caloric contents of food and drinks.
This article explains what calories are and how they compare with kcal and kJ, and also how to convert between the two.