I just travel on World Traveller recently. On the boarding pass, I found out that there was an "M" printed in the column CLASS.

I am quite sure that my booking class is not M. Then I google a bit just now. I also figure out that all first class pax got the code F, J for business class and M for Euro/World Traveler.

I was wondering, shouldn't Y be representing economy class instead of M? Or this M has some kind of a special meaning?

Thank you