It'll be the Treyarch developed title and will take place during various periods in history ranging from World War II, the Cold War, Vietnam and more secretive covert operations around the world.
This is most likely the title we all thought would be a Vietnam based shooter, but apparently will feature much more. It's also rumoured to release around October or November this year, but that's not confirmed.
What has also been rumoured, is the addition of a zombie mode, seen in World at War and the inclusion of dedicated servers for the PC version.
It all sounds very nice, but don't get too excited yet, it's all just hearsay.