BTU (British Thermal Unit) is a unit of energy that measures the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. This unit is commonly used in the United States and other countries to measure the heating or cooling capacity of appliances such as air conditioners, heaters, and furnaces. For example, an air conditioner with a capacity of 10,000 BTUs can cool a room of approximately 300-450 square feet.

BTUs are also used to measure the energy content of fuels such as natural gas, propane, and oil. For instance, one cubic foot of natural gas contains about 1,000 BTUs of energy.

In summary, BTUs are a useful way to measure the amount of energy required for different applications and appliances. It helps to understand the heating or cooling capacity of appliances and the energy content of fuels.