The Octane rating or octane number is a standard measure of the performance of a motor or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating. In broad terms, fuels with a higher octane rating are used in high-compression engines that generally have higher performance. Remember the air is already compressed by the turbo in forced induction engines. so there is a multiplier effect!

This means the higher the number the more the fuel can resist "pinking" (pre-ignition) and this very quickly destroys engines!