The term "energy unit" is often used in science to measure the amount of energy being used or produced. Synonyms for this term include "joule" which is the SI unit of energy, "calorie" which is a unit of energy used in nutrition, "BTU" or British Thermal Unit which is a unit of energy often used in heating and cooling systems, and "electronvolt" which is a unit of energy used in physics to measure the energy of subatomic particles. Other synonyms include "erg" which is a unit of energy used in mechanics and engineering, and "watt-hour" which is a unit of energy used in electricity consumption and production.