Galactic centre, the Galactic Core, (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe) or galactic zero centre, was a starting point for measurement used to determine the galactic coordinates of planets and locations. For example, Gallifrey was located at 10-0-11-0-0 by 0-2 from galactic zero centre (TV: Pyramids of Mars) while Miasimia Goria was located at 7-8-9-8-2-5-8-2-0-0 from galactic centre. (AUDIO: Planet of the Rani)
"Galactic Centre" was the centre of power for humans during the 24th century, (TV: The Happiness Patrol) also referred to as "Galactic Central" or "GalCent." (AUDIO: Bad Day in Tinseltown)
While trying to escape the Time Lords, the Second Doctor used a sextant to try and determine his position from Galactic Zero Centre upon arriving on a nameless planet in Galactic Sector 973. (PROSE: War Crimes)
The Saurians were from the galactic centre. (PROSE: Lords of the Galaxy)
The Daleks determined that the planet Spiridon would be a good staging post for their invasion of the galaxy, starting with the Galactic Core. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe, TV: Planet of the Daleks)
Sanukuma used the Last Great Time War as a distraction, and sent a SporeShip into the galactic centre to kill millions, before being stopped by the Eighth Doctor and River Song. (AUDIO: The Rulers of the Universe)