Cross realm means Qing against other realms.
On top of this, Blizzard also revealed their won’t be Battlegroups, which was actually just a hardware flaw back in the original Burning Crusade. Now, it’ll be region wide, everyone versus everyone in the arena. But a new problem will arise, how to handle Rank 1 titles. Blizzard has states they’ll probably be going with a percentage based system to reward the highest ranked teams. Hopefully we get ranked leaderboards back as well!
That’s from wowhead.