What does the term "fuel gas" refer to?

The term "fuel gas" primarily refers to gas that is utilized for heating, cooking, and various energy applications. This encompasses a wide array of gases such as natural gas, propane, and combustion gases which can be used in residential, commercial, and industrial settings for providing heat or as a cooking medium. The versatility of fuel gas makes it an integral component in everyday energy applications, hence supporting the designation of this option as the correct answer.

The other options, while related to specific gas applications, do not encapsulate the broader definition of "fuel gas." For instance, gas used primarily for industrial manufacturing is limited to a specific context and does not include its residential applications. Similarly, gases that are used exclusively for engine fuel exclude the myriad uses of fuel gas beyond automotive applications. Lastly, the reference to a high octane rating pertains specifically to fuels used in engines and does not relate to the general consumption of gas for heating and cooking.