Its primary planet is also named 'Tlor. It is the home of the Lumar race.
It is, essentially, entirely one gigantic city. The vast cityscape is one reason the Lumar have been unable to take full advantage of 'Tlor's wealth of resources.
From the Books: "‘Tlor was a grey, dismal place. Like Khatash, very little of the actual terrain could be seen from orbit. Unlike Khatash, this was because the Lumar homeworld was covered, nearly pole to pole, in densely crowded cityscape.
Nor was it interesting cityscape, Deluge reflected. The rows and blocks of buildings were of mostly uniform height and shape, giving the view a depressing sameness as he watched out the window of the orbital shuttle. His own ship was parked in a geosynchronous orbit just outside the cone-shaped Galactic Free Trade zone that extended up over ‘Tlor’s largest spaceport. He’d caught the shuttle down to the surface, and had enjoyed the exercise of blending in with the crowd on board.“ - Assassin, p.165.