The Homeworld was the ancient seat of the Great Houses.
The Homeworld of the Great Houses was sometimes called Gallifrey (TV: The Time Warrior) or Jewel. (COMIC: Return of the Daleks) In the City of the Saved, the term Houseworld — indicating both "world of the Houses" and "someone else's home" — was preferred, because among human species "homeworld" more often referred to Earth, and to avoid accepting the Houses' cultural imperialism. (PROSE: Of the City of the Saved...) "Houseworlder" was correspondingly substituted for "Homeworlder." (PROSE: Weapons Grade Snake Oil)
The Homeworld was the site of the caldera, where the thread of history was anchored. It stood in a special relationship to history, which made it no longer anything so simple as a planet. (PROSE: The Book of the War)
As a defensive measure shortly before the War, eight other planets were crypto-formed into versions of the Homeworld. This was called the Nine Homeworlds project. The rulers and residents of each naturally believed themselves to be the "true" one, and it was even possible that the Homeworld perceived to be occupying the centre of history was not the original. (PROSE: The Book of the War)