Define the term "octane rating."

The term "octane rating" specifically refers to a measurement of fuel's resistance to knocking during combustion. Knock, or pre-ignition, occurs when engine fuel combusts prematurely in the engine's cylinder, which can lead to engine knocking. The octane rating indicates how well a fuel can withstand compression before igniting. A higher octane rating means the fuel can endure higher compression without knocking, allowing for more efficient engine performance and potentially greater power output.

This is particularly important for high-performance engines, which typically require higher octane fuels to operate effectively and avoid engine damage. Thus, the definition linking octane rating with knocking resistance is the most accurate and relevant in understanding fuel performance characteristics.