Virgin reality

A sequence in the Seventh Doctor's life, broadly spanning his fight with the Timewyrm to his visit to the House of Lungbarrow, crystallized a version of reality into existence, (PROSE: Deceit, Blood Heat, Falls the Shadow, So Vile a Sin, et al.) known by some as the Universe (PROSE:  Genesys,  Apocalypse, Deceit) or the real universe because it was the only normal universe in existence. (PROSE: Blood Heat, No Future, Falls the Shadow, Dead Romance) Due to the process of crystallized time, other attributes of this reality included a version of human history leading into the Earth Empire, (PROSE: Blood Heat, The Dimension Riders) a version of Time Lord history involving looms, (PROSE: Cat's Cradle: Time's Crucible, et al.) the subsequent sequence of Bernice Summerfield's life on Dellah, (PROSE: Oh No It Isn't!, Ghost Devices, Dead Romance, et al.) and various other adventures of the Seventh Doctor's prior incarnations. (PROSE: The Crystal Bucephalus, The Well-Mannered War, A History of the Universe, et al.)

While the majority of sources indicated this reality was the same universe as the Doctor's universe as a whole, (PROSE: Vampire Science, Demontage, System Shock, Notre Dame du Temps, AUDIO: Enemy of the Daleks, The Prisoner's Dilemma, WC: Shadow of a Doubt, et al.) some indicated it was separate from other major strands of the Doctor's existence. (PROSE: The Eight Doctors, Interference - Book One, Dead Romance, Celestial Intervention - A Gallifreyan Noir, At Childhood's End, AUDIO: Auld Mortality, Signs and Wonders, et al.) One account implied it to be a possible timeline for the Doctor and Ace. (PROSE: At Childhood's End)

Origins
By many accounts, this reality was created out of crystallized time, with each landing of the Doctor's TARDIS crystallizing the visited events into certainty. (PROSE: Deceit, Blood Heat, Falls the Shadow, So Vile a Sin, et al.) Notably, an early event in this sequence of the Seventh Doctor's life brought him into contact with ancient Gallifreyan history, with the Doctor's communication with the 508th Pythia motivating her to unleash Pythia's Curse and initiate the version of history where Time Lords came from looms; (PROSE: Cat's Cradle: Time's Crucible) the Curse then rippled through the space-time fabric of the Doctor's present, indicating this too was a crystallized event which had not always been the single history. (PROSE: Transit)

One account showed that this reality was a bottle universe within the reality of the Eighth Doctor and the War in Heaven, created by I.M. Foreman by diverting part of "real" universe's Time Vortex into the bottle. (PROSE: Interference, Dead Romance) The phenomenon of time needing to be crystallised, by this account, was a sign of the bottle not containing enough biodata for a complete history. (PROSE: The Cosmology of the Spiral Politic)

Fate
By some accounts, this sequence of the Doctor's life continued into a sequence of the Eighth Doctor's life beginning with his travels with Sam Jones, (PROSE: Vampire Science, The Scarlet Empress) which some accounts held initiated a new version of reality. (PROSE: The Eight Doctors, Unnatural History) These accounts implied this to be the work of Rassilon behind the scenes; using the Eighth Doctor as his instrument of change, Rassilon claimed to have used the renegade to make "improvements to the pattern of history", (PROSE: The Eight Doctors) with a member of Faction Paradox claiming that he had changed time to ensure natural childbirth was not returned to Gallifrey, (PROSE: Unnatural History) as it was in the Seventh Doctor's time. (PROSE: Lungbarrow) However, the Book of Lies refused to confirm if these supposed changes "happened" in a traditional understanding of the word. (PROSE: Unnatural History)

Similarly, the sequence of Bernice Summerfield's Dellah life segued into her time with the Braxiatel Collection in an altered reality. (AUDIO: Professor Bernice Summerfield and the Mirror Effect, The End of the World, et al.)

Accounts dealing with this reality as a bottle universe indicated that the bottle quickly began to "leak" back into the reality which had created it, (PROSE: Interference) accounting for elements of this world's history existing in the Eighth Doctor's past. (PROSE: Vampire Science, etc.) It was fated to eventually break, after which the worlds in and out of the bottle would merge once and for all. (PROSE: Alien Bodies) Having been stolen by the Time Lords from Foreman, (PROSE: Interference - Book Two) the bottle was set adrift in the Time Vortex, which resulted in its contents spilling out. (PROSE: The Ancestor Cell) Subsequent accounts such as The Book of the War treated the events of Dead Romance as having very much taken place in the same reality as the War in Heaven. (PROSE: The Book of the War)

At any rate, by one account, the reality of the Eighth Doctor's travels with Sam Jones was itself rejoined with that of his travels with Destrii and with Charlotte Pollard as the Last Great Time War neared, such that all three existed in the Doctor's past from the perspective of the post-Time War universe as a mess of "jumbled" memories. (PROSE: The Eighth Doctor Part 2)

Relation to other realities
In Auld Mortality's universe, the Possibility Tree showed an alternative version of Gallifrey where the world was cursed and all the children died. (AUDIO: Auld Mortality)

The Seventh Doctor's interference on Earth in 2040 caused a new timeline which diverged from the native timeline of his companions, 30th century natives Chris Cwej and Roz Forrester. In the original 2040 timeline, a CIA-backed terrorist cell caused a nuclear explosion at Toronto's Pickering power station as a decisive step in America's takeover of Canada. The Seventh Doctor decided to change history by averting these events, using Cwej and Forrester to influence the terrorists and stop them while also publicly exposing the CIA plot. The new timeline took a period to stabilise, chaotically overlapping with the other reality, but it soon stabilised. (PROSE: The Nuclear Option)

The Aubertides pursued the Seventh Doctor to England prior to the First World War, where he was disguised as a human teacher named John Smith. (PROSE: Human Nature) A similar incident occurred when, in the post-Time War universe, the Tenth Doctor became John Smith in an attempt to elude the Family of Blood. (TV: Human Nature/The Family of Blood) Daughter of Mine, of the Family of Blood, was aware that this was a "story that happened many times in many ways", not all of which she was present for. (AUDIO: Shadow of a Doubt)

By one account, Ace was shown multiple possible futures in her timeline by a Quantum Anvil, which included travelling in the TARDIS with a dark haired woman, fighting Daleks and living with an ancestor of Sorin. According to her memories, this incident led her to leave the Doctor. (PROSE: At Childhood's End)

Behind the scenes

 * Early Big Finish Productions stories featuring Bernice Summerfield were branded as Side Steps into "Virgin territory". Later stories dropped this branding.
 * Steven Moffat has described the Virgin New Adventures as "a separate (and equally valid) continuity" to the modern BBC Wales TV series.