There was some mention of this term on another thread. I'd always assumed it was someone who partakes of their chosen sport [biking, kayaking, whatever] on occasional weekends, rather than someone who does it more often. I guess by definition the people doing it more often are likely to be doing it for a living.
Then the impression I got was that its real/common meaning was someone who just wasn't very good.
There will of course tend to be some correlation between people who don't bike very often and people who aren't very good, but not in all cases.
So what does it really mean?