The term fuel refers to a substance that is burned or used as energy in engines, furnaces and other machines. Fuel use means using this substance for generating power through combustion or chemical reactions. This can include burning gasoline, diesel, natural gas, coal, wood or any other source of energy to produce heat or electricity. In the transportation sector, fuel is used in internal combustion engines to propel vehicles while in industrial settings it may be used for heating and power generation. The amount of fuel used can vary depending on factors such as efficiency, demand, cost, availability and technology. Reducing fuel use through energy conservation measures or the development of more efficient technologies is an important goal towards reducing greenhouse gas emissions and mitigating climate change.