Ok are these two names for the same game or are they completely different games which will be made? Is Fallout 4 the official next game and New Vegas a spinoff? Im so confused

There are two topics dedicated to these two new games.

http://www.gamesas.com/bgsforums/index.php?showtopic=1045768

http://www.gamesas.com/bgsforums/index.php?showtopic=1046887

Please use them to find out and discuss. Thanks.