Fuel

A fuel is any material that can react to provide energy in a useable form instead of a potential form. In most cases this is just somthing that will burn for example coal was burnt by steam trains to heat water to provide power, or gas is burnt to provide heat to run power plants. however a fuel is not necessaraly combustable for example in a nuclear reaction a fuel will under go fission this still provides a useable source of energy but not via combustion.