Originally Posted by JohnFortWorth
"C" is universally a booking class for Business, like "F" for First and "Y" for Coach. I think the code was originally used by Pan American to identify "Clipper Class", the first business class with its own cabin, launched in the late 1970s.
J might be thought of today as more universal at least in North America, though a lot of Latin American airlines like COPA and TACA call business C.
Anyway on AA it is international Y to J upgrade.