I don't understand why other phones have to be dragged in the comments here.
As far as I understand, it would mean you could play multiplayer games on 2 phones(at least one of them being WiFi Direct), WITHOUT connecting to an external WiFi network. All you need to do is enable WiFi Direct on your phone, connect to the other, and play!
Do let me know if I've misunderstood.
P.S.: It's not like JoikuSpot or WiFi tethering. These options make your device behave like a Router.