British Thermal Unit (Btu) is the heating unit used to measure the heat output in a range. It's the amount of heat you require to increase the temperature of one point of water by a single Fahrenheit.
BTU is the amount of heat a burner in your stove puts off. For instance, you can have a kitchen range with Btu ranging from 650 Btu to 18,000 Btu. The average Btu for kitchen ranges is 7,000 Btus.