Outback was a term used during the Web Era to refer to those worlds not connected to the WorldWeb via farcaster, or with only limited access to the farcaster network. Those worlds were normally only reachable by regular space travel, meaning any travelers there would accumulate Time Debt to arrive. Outback worlds could become part of the Hegemony of Man via a long process that included these planets submitting to the Hegemony as part of its Protectorate, and the ascent of the Senate and the All Thing.
The planet of Hyperion was an Outback world. Many years before the Final Shrike Pilgrimage, Brawne Lamia's father, Senator Lamia, attempted to integrate Hyperion into the Web, a move that was unsuccessful in part due to the absolute opposition of the TechnoCore, who was obsessed over the planet as being an uncertainty in its predictive calculations.
For a complete list of all known Outback worlds, see Category:Outback.