When searching for trades on the GTS, I see a lot in the notes from Japanese (and Korean players, too) players indicating Pokemon IVs by different letters: A, B, C, D, H, S, like:
HCDS4v
I usually don't know what I get until I do the trade, but sometimes I'm looking for something specific, like a Ditto with certain stat values and like to know what I would be getting beforehand.
Which stats correspond to which letters? How do I know if they are offering or wanting something?