The different ways to lable the gasoline.
https://www.etuners.gr/fuel/Higher octane will not harm the engine, too low can. Different with newer cars with knocking sensors that adapt the fuel injection and ignition to the bad or good fuel.
Our old bikes have only us to supervise how engine like the fuel or not. Bad idea to retard ignition before using higher octane and harvest the built-in power.
From the link above....
Europe vs the States
In Europe, gas stations describe different types of gasoline based on their RON rating. It is typical to have 100, 99, 98, 97 or 95 RON with prices varying accordingly. In the States the descriptions look a lot like RON, but they are not.
Pump gas
In the United States gas stations describe the types of gasoline based on the Pump Octane Number (PON). That number is the average between RON and MON. This causes many problems.
If a fuel is 98 RON then it will be 93 PON -> 93 PUMP
If a fuel is 95 RON and 87 MON then it will be 91 PON -> 91 PUMP