P-G:
When I search "Access Code" on this board, I find that it seems to have something to do with the brainking app. That's all I found about it. It's been about 10 years since it was last mentioned.

Right under the "Access Code" of your profile, it says : "Access code is your unique identification string (generated by BrainKing). If you are using third party products to access BrainKing, you might be asked for this code to confirm your identity. This is NOT your BrainKing password, so there is no risk of accessing your private data if you provide this code to external programs.
(*) - invisible to other players"

P-G: It used to be something for a Facebook app which is no longer active (and hadn't been developed by us). You can just ignore it.