The Five Galaxies were a group of galaxies that included the Mutter's Spiral. By 2007 Earth was referred to as "the most frequently attacked, colonised, exploited and enslaved planet in the five galaxies". (PROSE: Borrowed Time)
At some point after 1959, the Confederation existed in the five galaxies and set up the toll ports, (PROSE: Delta and the Bannermen) including G715 which was used by Nostalgia Tours. The Seventh Doctor told Mel that Nostalgia Tours was "the most notorious travel firm in five galaxies." (TV: Delta and the Bannermen)