Loom

Looms or breeding-engines were devices used by the Great Houses of the Time Lords to perpetuate their race. (PROSE: Cat's Cradle: Time's Crucible, The Book of the War) Unable to procreate sexually, the Time Lords had to rely on these Rassilon-invented devices (PROSE: Cat's Cradle: Time's Crucible) to "weave" new life from base matter and biodata. (PROSE: The Book of the War)

Description
Each Great House on Gallifrey had their own Loom which they used to create new members of their Family. (PROSE: Cat's Cradle: Time's Crucible, Lungbarrow) Each of these breeding-engines was kept outside the corresponding chapterhouse in a loomshed, where they would whisper to each other in the night. (PROSE: The Book of the War)

The breeding-engines were slightly prescient, but not enough to weave a newborn's entire life story into their biodata. (PROSE: The Book of the War) During looming, childrene were primed with foreknowledge through memetic priming. (PROSE: Against Nature)

The genetic relationship between people originating from each Family Loom was lateral rather than direct, meaning that people from the same Loom were "cousins" of each other. Gallifreyans were loomed as "full-grown adults", albeit ones that began child-like and had to mature mentally. (PROSE: Lungbarrow)

Members of a Great House were loomed to full physicality but lacked the experience of the elders, so they were called childrene (PROSE: Against Nature) or "loomlings." (PROSE: Unnatural History) Leela felt pity for Gallifreyans, saying that the Looms prevented "true children" from existing on their planet. (PROSE: Lungbarrow) According to one account, upon being Loomed into the House of Lungbarrow, the Doctor was physically in the form of a child. (PROSE: Human Nature) Some childrene, while being mentally or emotionally older, apparently did physically resemble children (PROSE: Of the City of the Saved...)

Looms also kept a tally of all the people they birthed, and could normally indicate how old each of its "offspring" was and how many regenerations each had gone through. Data from all the Family Looms on Gallifrey was sent to the Bureau of Loomographic Records, which served as a central repository of genetic information.

Each Great House had a specified number of cousins which could exist in the Family at any given time. The House of Lungbarrow, for example, was allotted forty-five cousins. When a member of a Family died for the final time, the Loom would weave a new cousin into the Family. Cases did exist when an additional cousin was illegally woven, such as the Doctor's cousin Owis, but these were extremely rare. (PROSE: Lungbarrow)

Remembrance tanks were "parodies" of breeding-engines. (PROSE: The Book of the War) Sontarans were also created by looms. (PROSE: The Infinity Doctors)

History
In the time of the anchoring of the thread, (PROSE: The Book of the War) Rassilon created the Looms to stabilise the Gallifreyan population after they were rendered sterile by Pythia's curse. One was given to each Great House. (PROSE: Cat's Cradle: Time's Crucible) These breeding-engines were designed to produce generations of flawless academicians and observers, and they did so for ten million years. (PROSE: The Book of the War)

However, there were instances of womb-born children during the period where Looms were in use. Rassilon passed a decree that "only the Loom-born shall inherit the Legacy of Rassilon", and enforced this decree by wiping out the womb-born. (PROSE: Cold Fusion) However, some womb-born survived this persecution and hid among the general population for hundreds of centuries. (PROSE: The Infinity Doctors)

Despite their supposed infallibility, mutations began to appear in the breeding-engines twelve hundred years before the War. This resulted in a generation of renegades that included the Imperator, Grandfather Paradox, and the War King.

The Order of the Weal was interested in unstable bloodlines, and The Book of the War hypothesised that the Order made subtle alterations to the programme dynamics of the Houses' engines.

Loomstacks on Gallifrey Eight were used to mass-produce soldiers during the War. (PROSE: The Taking of Planet 5) It was feared that the enemy's influence could retro-compromise the Houses' soldiers and affect the nature of their breeding-engines; this exact phenomenon may have caused the Sixth Wave to retro-annul itself at birth or to be born supporting the wrong side.

In the Rivera Manuscript, the enemy's attack on the Homeworld made the breeding-engines continuously scream from the loomsheds. The enemy soldiers eventually attacked the engines directly, detonating themselves and leaving the looms intact but mutated. These mutations spread as a sickness throughout the survivors of the attack. (PROSE: The Book of the War)

When Rassilon and the Cybermen conquered Gallifrey, they used Looms to trap captured Time Lords in a state of perpetual regeneration, where the Looms could harvest the energy created. The Cybermen later linked it to the Cyberiad and the Eye of Harmony, where they planned to alter history. The Twelfth Doctor and Rassilon countered this plan by using the energy to regenerate the universe and return history to normal. (COMIC: Supremacy of the Cybermen)

The Doctor
When he was only five years old, the Doctor boasted that he could remember existing in the House of Lungbarrow's Loom before being actually born:

"I can remember waiting to be born... It was like being all strung out. All unravelled inside the Loom. I was spread really thin... I couldn't think. Not put thoughts together... But I knew where I was and what was happening. I couldn't wait to get out. And then I was born. My lungs nearly burst. The first rush of air was so cold...""

- The Doctor

The Eighth Doctor remembered both being loomed and having parents and a childhood. (PROSE: Unnatural History, The Shadows of Avalon) He knew that one of these was a dream, but he could not recall which. (PROSE: The Shadows of Avalon) The boy from Faction Paradox suggested that the enemy was rewriting the Doctor's past "when he wasn't looking". (PROSE: Unnatural History) In one universe, the Doctor believed he had been "born of the Loom, son of the greatest explorer of his age and a human woman." (PROSE: The Infinity Doctors)

Behind the scenes

 * Like many ideas and concepts in Doctor Who, this has not been referenced on-screen, and can be seen to contradict other sources. There have been many statements by the Doctor and others referring to him being a "boy" or showing the Doctor and other Time Lords as children.
 * In his production notes in DWM 482, Steven Moffat, while obliquely referring to this discrepancy, claimed that it was "reasonable to assume that Time Lords [met] and marr[ied] and mate[d] in much the same way" humans did. He acknowledged "some highly inventive material in the Virgin New Adventures books contradicting this" and described the New Adventures as "a separate (and equally valid) continuity" to the modern BBC Wales TV series.
 * Lance Parkin's short story Executive Action, published in Walking in Eternity, contains further details to the conflict between Loomed and Womb-Born seen in Cold Fusion and referenced in The Infinity Doctors. It is revealed that Loomed Gallifreyans are considered "pale imitations" to the Womb-Born, with considerably weaker mental powers, suggesting that Rassilon instigates the forced social change to ensure no Time Lord becomes more powerful than he.