what is octane????

Gasoline is a mixture of hydrocarbon chains, which are named for the number of carbon atoms linked together to form the chain.

These include heptane (5 carbon atoms), hexane (six), septane (7), octane (8), nonane (9), and others.

Octane is desirable in a motor fuel because of its explosive properties. Other familiar names of carbon chains include methane (4) and propane (3).

For much more information, including diagrams and more complete descriptions, try an internet search on "octane," or on "carbon chains."

That is also a good idea because it's been a long time since I took organic chemistry, and I might be wrong about some of the names and numbers.

PS: Octane occurs naturally in liquid form, rather than as a gas.

The simplest explanation is that it's gasoline's ability not to spontaneously ignite.
The higher the octane number the greater the ability not to sponateously ignite.Cars that require higher octane fuels have engines with higher compression ratios.
In english what that means is as a fuel is compressed into a smaller space it's going to get hot and the objective is to have that fuel be ignited by the spark plug and not as a result of heat created by compression.
The classic sound of an engine in need of a higher octane fuel is some times referred to as a knock. Essentially it's the sound of fuel igniting twice in a very short period of time : once when it's not supposed to and once when it's supposed to and it's bad for engines.
Having said that if your car doesn't require high octane fuel and your engine is giving you no indication that it does then don't buy it because it's a complete waste of money

Its a hydrocarbon based fuel used to compare various gasoline mixtures, mainly on their rates of combustion. A 100% would mean there is no "knock" or in other words an high combustion rate. The importance of "knock" is that an uneven fuel burn rate in the cylinder would create unburnt fuel and a jerky crankshaft rotation. The smoother the engine runs, the less wear and tear there is on the parts.

Diesel fuel uses "cetane" as its standard.

Octane is a gas that when mixed with heptane, you get automotive gasoline, the octane level is determined by the ratio.