Definition
A numerical measure of an aviation gasoline's resistance to detonation (uncontrolled, premature combustion) inside an engine cylinder. A higher octane rating means the fuel can withstand greater pressure and temperature before detonating. Aviation gasolines are commonly identified by two ratings (e.g., 100/130), where the lower number applies to a lean fuel-air mixture and the higher number to a rich mixture.
Plain English
A number that tells you how well a fuel resists exploding on its own from heat and pressure inside the engine. The higher the number, the more pressure the fuel can take before it misbehaves.
Context Anchor
Seen in aircraft fuel grades, engine operating limits, aircraft manuals, and maintenance discussions about approved fuel.
Derivation
From octane, an eight-carbon hydrocarbon (Latin octo, 'eight') used as the reference fuel in early anti-knock testing. The scale was built around how a test fuel compared to pure octane, and the name stuck even though modern avgas contains many other compounds.
Why Pilots Care
Selecting the correct octane rating prevents engine damage from detonation and ensures reliable performance under varying power settings.
Analogy
Octane rating is like a heat-and-pressure tolerance label for the fuel. It does not say the fuel has more energy; it says the fuel is harder to make burn the wrong way.
Intuition Check
Higher octane does not mean the fuel gives more power by itself. It means the fuel is more resistant to harmful early or uncontrolled burning inside the engine.
Example Sentence 1
The engine data plate calls for 100-octane avgas, so the pilot confirmed the fuel truck was dispensing 100LL before refueling.
Example Sentence 2
The engine manual specified a minimum octane rating to avoid detonation during takeoff power.