Certain airlines have different name for their classes. in AWS we use F, C and Y but some also uses J, E and M classes. In all cases I have not been able to find what these Class Codes actually mean?
Airlines usually subdivide their travel classes (First, Business, Economy) into separate booking classes. So for example Lufthansa uses booking classes Y, B, M, H, X, V, W, Q, S, G, K, L, T, E, U for Economy Class; C, D, I, J, Z, P for Business Class and A, F, O for First Class.
They are -roughly said- each priced differently and activated at different times according to time until the date of the flight and demand. Very roughly, the next most expensive is activated once the cheaper booking class is booked out (there is a contingent for every one). It's much more complicated than that, but just so you get the general idea. Some booking classes are also reserved for frequent traveler awards or employee travel. They don't 'mean' anything in that sense.
Well, as you can see from the above, there is one booking class denominating the full fare. For LH, that's F, C and Y. So those are used as general 'codes' for the travel classes. Some airlines use J as their full fare Business Class code, but F and Y are basically the same for pretty much every airline in the world.