Extranet

Origin:
The extranet was spawned during a line of jokes relating to Dec69's activities with Elites (Sangheili) on Halo: Reach, after Doc noticed a trend in injuries (Or the location of them) on Dec's person when he came into the clinic regularly. Following a hunch, Doc searched the extranet a bit and found a multitude of videos depicting Dec having various forms of intercourse with the majority of the races in the Covenant.

The Extranet has since become used to describe the in-game version of the internet, and though it is not technically accessible within the bounds of the games themselves, it is implied that the characters access it regularly.

Bonus:
The name Extranet originates from the Mass Effect universe.