If you've ever wanted to have a friendly match strictly for bragging rights, try out a new prospective arena or BG-mate before committing, or just practice some strategies, then war games are for you. Instead of accidentally almost starting a nuclear firestorm by playing games with a computer, you'll be skirmishing against other players in the World of Warcraft.
While these matches are not for points, they can allow you to do fun things like challenge a rival guild to an Alterac Valley free-for-all, set up some arena runs to iron out the kinks in your group composition without losing rating, or set up an in-realm tournament on your own time. All war games must be between players on the same realm, but combatants can be from the same or different faction.
We used to set up complicated free for alls in the Gurubashi Arena in guild for fun nights, this seems like a good way to extend that tradition. Go check out the complete FAQ and see if it's for you.