Galaxy

According to the Tenth Doctor, universes such as N-Space contained millions, (TV: Planet of the Ood) potentially trillions of galaxies while constantly expanding. (PROSE: The Last Dodo) The Tiberian spiral galaxy, for one, contained a million star systems, a hundred million planets, and a billion trillion people when it was destroyed. (TV: Nightmare in Silver) Rarely, galaxies were also known as island universes. (PROSE: The Sons of the Crab)

Types of galaxies
Pin galaxies were galaxies which existed within the universe of the atom. They were difficult to study as they only had a life span of about one attosecond (a quintillionth of a second). (TV: The Two Doctors)

Satellite galaxies, also called dwarf galaxies, were small galaxies that orbited larger galaxies. They contained many stars, but not as many as a larger galaxy. (PROSE: The Eyeless, AUDIO: The Last Voyage)

The Tiberian galaxy was an example of a spiral galaxy. (TV: Nightmare in Silver)

A terminus galaxy was, according to the Ninth Doctor, a "jumping-off point for a lot of places". (PROSE: The Beast of Babylon)

Galaxies designated as junk galaxies were home to junk planets. (TV: The Tsuranga Conundrum)

Named
Most of the Doctor's adventures took place in the galaxy known to the Time Lords as Mutter's Spiral, (TV: The Deadly Assassin) although he was also known to have visited other galaxies such as the Andromeda Galaxy and the Isop Galaxy. (PROSE: Alien Bodies, TV: Castrovalva, The Web Planet)

The Magellanic Clouds were two dwarf galaxies, called the Larger Magellanic Cloud and Smaller Magellanic Cloud. They were in galactic orbit around Mutter's Spiral. (AUDIO: The Last Voyage)

The Acteon Galaxy, or Acteon Group, (PROSE: Tragedy Day) was the galaxy in which Metebelis III was located. (AUDIO: Worldwide Web)

The Aktren Galaxy was the location of the Klytode homeworld. (COMIC: The Snag Finders)

The Tenth Doctor named a galaxy Alison. (TV: The End of Time)

The Amron Ho galaxy contained the asteroid of Primo Temp. (COMIC: Buying Time)

Zeta Minor was twice as distant from the Artoro Galaxy as that galaxy was from the Anterides. (TV: Planet of Evil)

Brouhaha-Nine-Nine-Five was the location of Buchan Industries and the Ever-and-Ever Prolixity. (AUDIO: The Lamentation Cipher, The Viyran Solution)

Casta Pizellus was a galaxy known to the Doctor. (PROSE: I Am a Dalek)

Urlic was the last planet of the Catorkian Galaxy by 2050. (TV: Lost Library of Ukko)

The Crab Galaxy was home to the planet Proxima Centauri. (COMIC: Ride to Nowhere)

The Ellemede Galaxy was the galaxy in which Jora and Vyre were located. (PROSE: Syntax, Illumination)

The Emphidian Reach was a galaxy where the Doctor fought Dalek stealth ships in one of its arms. (COMIC: Selfie)

The Enclave was a pocket galaxy which connected the Obverse to the wider universe. (PROSE: The Ancestor Cell)

The Fraxis Galaxy contained the constellation of Zandrobar and the planet Zorth. (AUDIO: Tartarus)

The Gelidus Galaxy was the galaxy of origin of Karina Stirling. (COMIC: Station Zero)

The Helical Galaxy was the location of the twin planets Atrios and Zeos. (TV: The Armageddon Factor)

The Illia galaxy was a nearby galaxy to Gallifrey. (PROSE: Pandoric's Box)

The Keeba galaxy was home to the Keebans. (TV: The Tsuranga Conundrum)

Kinrexian was a galaxy that supported life of some kind. (PROSE: The Last Dodo)

The galaxies M82, M83 and M84 all supported life of some kind. (PROSE: The Last Dodo) M87 was home to the planet that would become New Earth. (TV: New Earth)

Whilst travelling with the Tenth Doctor, Donna Noble witnessed the destruction of the Mestophelix Galaxy. (COMIC: The Widow's Curse)

The Metasaran Galaxy was the location of Sontar, the homeworld of the Sontarans. (TV: The Last Sontaran)

The Ogidi Galaxy was the galaxy that the Brilliant was travelling in when it was attacked by the Mandelbrot Sett. (PROSE: The Pirate Loop)

Pangloss was a galaxy that contained the planet Olleril. (PROSE: Tragedy Day)

The Pheezel Galaxy was the location of Seacyde. (COMIC: The Shark Shocker)

The Phi-Ralix galaxy was one of the Ten Galaxies. (PROSE: Mutually Assured Domination)

The Platrion Galaxy was the location of the Gates of Martontigan. (PROSE: Revenants)

The Pristatrek Galaxy was the location of Olleril. (PROSE: Tragedy Day)

QSO 0046 was the home galaxy of Kirith in the far future. It was one of the Ten Galaxies and was located at the very edge of the explored universe. (PROSE: Timewyrm: Apocalypse)

RE 1489 was a galaxy in which the planet Urbanka and its sun Inokshi was located. (TV: Four to Doomsday)

The Daleks recreated the Seriphia Galaxy with the Apocalypse Element and used it as their main base of operations during their invasions of Mutter's Spiral. (AUDIO: The Apocalypse Element, Dalek Empire)

The Silfrax Galaxy was the home galaxy of the Vespiforms. (TV: The Unicorn and the Wasp)

The Thunderhead Spiral Galaxy was a galaxy inhabited by the Prastaki. (PROSE: Day of the Clown)

The Tiberian spiral galaxy was a galaxy sacrificed by the human empire to destroy all Cybermen, bringing the Cyber-Wars to an end. The human emperor, Ludens Nimrod Kendrick Cord Longstaff XLI, ruled a thousand galaxies. (TV: Nightmare in Silver)

The West Galaxy was the location of the Generios system. (AUDIO: The One Doctor)

The Wrarth Galaxy was a galaxy on the other side of the universe from Mutter's Spiral, inhabited by the Wrarth Warriors and the Meeps. (COMIC: Doctor Who and the Star Beast)

Numbered
Galaxy Three was a galaxy containing the planet Wrechon Four and the Ninexie homeworld. (AUDIO: Absolute Power)

The Third Galaxy was the galaxy in which the planets Urbinia and Baralda were located. (AUDIO: Daughter of the Gods)

The planet Drahva, home of the hierarchical, feminine-appearing Drahvins, was located in Galaxy 4. (TV: Galaxy 4)

The Fourth Galaxy was one of the Outer Galaxies. (TV: The Daleks' Master Plan)

The Dragonhunters had breeding grounds in Galaxy Five. (AUDIO: And You Will Obey Me)

The Fifth Galaxy was one of the Outer Galaxies, represented at the Galactic Council by Zephon, its Master in 4000. (TV: The Daleks' Master Plan)

Galaxy 7 was a galaxy that contained the planet Hedenex, home to the Hedenexians. (AUDIO: Benny's Story)

The Seventh Galaxy, also called the Sculptor Dwarf Galaxy, (PROSE: The Eyeless) was a part of the Seven Galaxies (TV: Genesis of the Daleks) located 290,000 light-years from Earth. (PROSE: The Eyeless) According to one account, it was the location of Skaro, the Dalek homeworld. (PROSE: The Infinity Doctors)

The Seventh Spiral Galaxy was the galaxy where the Koth-Kulaar originated. (COMIC: The Moon of Lost Hope)

According to one account, the Eighth Galaxy was the location of Skaro. (AUDIO: The Destroyers)

The Tenth Galaxy was the largest of the Outer Galaxies, represented by Trantis on the Galactic Council. (TV: The Daleks' Master Plan)

The Thirteenth Galaxy was a galaxy where the thirteenth planet was located. (COMIC: Triskaidekaphobia)

The 29th Galaxy was a galaxy where Kerun Za was located. (COMIC: Sea-Rah)

Galaxy 57 was the galaxy in which Usunru was located. (COMIC: The Cleverest King)

Galaxy 357 was a galaxy inhabited by the cloud hangers. (AUDIO: I Am The Master)

Unidentified galaxies
A small galaxy was contained within the star chamber, a room in the Doctor's TARDIS. (AUDIO: Persuasion)

Eugene Jones supposedly "worked out" which galaxy the Dogon Sixth Eye hailed from. (TV: Random Shoes)

According to Jack Harkness, the space whale known as "Cash Cow" hailed from a galaxy beyond Mutter's Spiral. (TV: Meat)

Sarah Jane Smith observed that Erasmus Darkening hailed from a galaxy other than Mutter's Spiral. (TV: The Eternity Trap)

The Bank of Karabraxos was promoted as the greatest and most secure bank in "the galaxy". (TV: Time Heist)

Groups of galaxies
The Tri-Galactic was a trio of galaxies, including Mutter's Spiral, in which the Second Great and Bountiful Human Empire was active around the 42nd century. (TV: Planet of the Ood)

The Five Galaxies were a group of galaxies which included Mutter's Spiral. (PROSE: Borrowed Time, TV: Delta and the Bannermen)

The Seven Galaxies were a collection of galaxies near and at the centre of the universe. (TV: Twice Upon a Time) The Kaleds believed that Skaro, which existed in the Seventh Galaxy, (PROSE: The Infinity Doctors) was the only planet capable of supporting life in all of the Seven Galaxies. (TV: Genesis of the Daleks)

The Nine Galaxies were a group of galaxies. (PROSE: Fascination, AUDIO: The Dispossessed)

The Ten Galaxies were a group of galaxies ruled by the Dominators and their Quark servants, calling themselves the "Masters of the Ten Galaxies," (TV: The Dominators) although the claim went unchallenged (PROSE: Mutually Assured Domination) and William Bishop later wondered if it was simply propaganda. (PROSE: The Two Brigadiers) Among the galaxies were Phi-Ralix, the Dominators' home galaxy, the Mutter's Spiral (PROSE: Mutually Assured Domination) and, in the far future, the galaxy QSO 0046. (PROSE: Timewyrm: Apocalypse)

The Twelve Galaxies were a group of galaxies. (TV: Dragonfire, The Ghost Monument)

The Alignment of Exodor were seventeen galaxies in perfect unison. (TV: Closing Time)

In the year 4000, the Daleks held a meeting with representatives from seven Outer Galaxies to plot the invasion and overthrow of human-occupied space. By that time, they had already taken over at least seventy planets in the Ninth Galactic System. (TV: Mission to the Unknown)

The Time Lord Duotheros studied humanoid races in the rim galaxies. (AUDIO: The Wings of a Butterfly)

The Vegas Galaxies were a group of galaxies. (TV: Kiss Kiss, Bang Bang)

Fate
In N-Space, the galaxies had collapsed by the end of the universe in the year 100,000,000,000,000. The Tenth Doctor told Professor that, had he been in a different time, he would have been revered throughout the galaxies. (TV: Utopia)

Intergalactic
Organisations which operated intergalactically included the Intergalactic Flora Society, (PROSE: The Room With No Doors) the Intergalactic Floral Society, (TV: The Seeds of Doom) Intergalactic News (COMIC: Terrorformer) and the Intergalactic Union of Pan-Dimensional Assistants and Companions. (PROSE: Project: Wildthyme)

Intergalactic law spanned galaxies, (TV: Carnival of Monsters) as did the intergalactic rules of engagement, (TV: The Poison Sky) the Intergalactic Olympic Games, (PROSE: Placebo Effect) the Intergalactic Song Contest, (AUDIO: Bang-Bang-a-Boom!) the Intergalactic Staring Championship (PROSE: Ghosts of India) and the Intergalactic Treaty of Cultural Rights. (COMIC: Echo)

The Thirteenth Doctor identified the Judoon as intergalactic police and mercenaries. (TV: Fugitive of the Judoon)

Other references
In 1958, Lord Azlok boasted that the Viperox had laid waste to entire galaxies. (TV: Dreamland)

The Eleventh Doctor noted that Saborian smelling salts were outlawed "in seven galaxies", (TV: The Power of Three) while magno-grabs were outlawed in "most galaxies". (TV: Journey to the Centre of the TARDIS)

The Moment was known as the "Galaxy Eater". (TV: The Day of the Doctor)

Davros reflected that galaxies had burned in the time that he and the Doctor knew each other. (TV: The Witch's Familiar)

Behind the scenes

 * In PROSE: The Sons of the Crab, galaxies are referred to as "island universes", which is an archaic term, originating in the nineteenth century, and going out of fashion in the early twentieth.