Thanks for the quick - and helpful - response Jasper!
So if I'm following you then basically the three 'main' classes of tickets I'm used to seeing (economy, business, 1st) are further subdivided? And this further division is related to the flexibility and 'perks' associated with the particular class as opposed to physical difference (i.e. location in the plane)?
If that's correct then I'm wondering if all the airlines use the same, or at least similar, fare class designators? As I look at the AA fare classes they have 3 in First Class (A, F, P), four in Business (D, I, J, R), and whole slew in various levels of Economy Class... is there a pattern/meaning here or do they just mix up the alphabet and shake a random selection of letter into each fare class???