The Reclaimer Trilogy

The new Halo series, starting with Halo 4 is to be known as The Reclaimer Trilogy. 

It's basically final confirmation that the Chief will be up against Forerunner tech....

Out of the Halo Fest:

"He said that with the Chief headed toward a mysterious new planet, the team is investing heavily in the look and feel of the Forerunner civilization. O'Connor chimed in, saying that players have seen inert, abandoned Forerunner structures in the past, but now they'll see what that technology looks like when it isn't completely dead."

"Halo 4's story is still being closely guarded, but O'Connor did emphasize that the game will be a direct sequel to Halo 3, and that it deals with the fate of Master Chief and Cortana."

And seeing as the Chief is a Reclaimer, it makes sense for the series of games to be known as the  Reclaimer Trilogy