Account-wide achievements are achievements introduced with the Mists of pandaria expansion that can include criteria fulfilled by multiple characters on the same Battle.net account and in the same region.
Available at the Battle.net account level, as such, would apply to all of the attached World of Warcraft licenses on the account.
Won't be tied to game licenses. Not sure if these means achievements will count between PTR and Live.
Intended to be an overall change to the current achievement system.
Will be available to players without Mists of Pandaria.
Q. Will there be account-wide Achievements? If so, can we expect to see things like vanity gifts for having multiple characters?
A. It’s an idea we definitely want to do, but it’s pretty challenging technically, so it’s not on the immediate horizon. We can’t promise anything obviously, but I wouldn’t feel the need to get difficult Achievements on more than one character on the same account.