
In General Ledger 11i your functional currency referred to the currency of your set of books, it was one of your three Cs (Calendar, Currency and Chart of Accounts). In R12 we changed the terminlogy, there is no more set of books that is now renamed Ledger and the Currency of your Ledger is referred to as the Accounting Currency of the Ledger.
This is a subtle change and I'm sure experienced 11i practitioners are still using the term functional currency but you all need to stop because it's confusing people.
In Financial standards (IAS 21 and FAS 52), Functional Currency is a test