I think it's difficult to quantify it really.......because it's different things to different people.
Like me and @Renegade ......he's always been into the club and rally scene. Whereas I've got no interest in that.
I was always more into going to race meetings etc......the sport side of things. Whereas he wasn't.
So it's a case of people participating in the elements of motorcycling that appeal to them.
But, underpinning it all, must be a love of motorcycles. If you don't have that then you're not a biker in my opinion.