Terradon was a planet in E-Space. (TV: Earthshock)
History[]
The Terradonians were natives of the planet. The Alzarians, who evolved to believe themselves Terradonians, intended to fly the Starliner to Terradon. With the Fourth Doctor's assistance, they were able to operate the craft. (TV: Full Circle)
When Adric and the Fifth Doctor argued over Adric's claim that the Doctor didn't pay attention to him, Adric demanded that the Doctor take him home to Terradon; the Doctor was reluctant to re-enter E-Space, and told him so. (TV: Earthshock)