Joules
The joule (J) is the SI unit of energy, named after the English physicist James Prescott Joule. It is the work done when a force of one newton moves an object by one meter in the direction of the force, so it is sometimes known as a newton-meter. It is also one watt-second.
Calories (15 °C, NBS 1939)
The 15 °C NBS 1939 calorie is the amount of energy required to raise the temperature of one gram of water by one degree Celsius, from 14.5 °C to 15.5 °C, at standard atmospheric pressure. This specific definition was established by the National Bureau of Standards (NBS) in 1939.