Calorie

Definition
A calorie is defined as the amount of energy that is required to raise the temperature of 1 liter of water by 1 degree Celsius. (It is important to note that we are referring to food calories and not individual calories and that 1 food calorie is equal to exactly 1,000 calories.)

Calories
Calories in food are not nessecarily good or bad. But some food that is high in calories is said to be unhealthy or even toxic in large quantities.