Btu - (n.)
British Thermal Unit is a unit of energy (energy is the ability to do work). The definition for Btu is the amount of energy required to raise the temperature of 1 pound of water 1 degree Fahrenheit (°F). Practically speaking, a Btu is equivalent to about the heat from a kitchen match. The unit 1 quadrillion Btu (1015 Btu) is often used for reporting fossil fuel use.