Doctor Who universe
The Doctor Who universe, or Whoniverse, is a term used by fans, and increasingly the mainstream press, to describe the shared fictional universe in which the stories of Doctor Who, K-9 & Company, Torchwood and The Sarah Jane Adventures are set.
Semantic origins
The term "Whoniverse" has its origins at least as far back as the 1983 BBC book, Doctor Who: A Celebration by Peter Haining. At that time, the Whoniverse had a very broad meaning, which included not just the setting of Doctor Who stories, but everything about the series, including behind-the-scenes information and fandom itself.
Current usage
"Whoniverse" gradually became a more specific term, at first used as a way to emphasize that Doctor Who stories told in other media were part of the same universe as those told on television. In the BBC Wales era, more aggressive steps have been taken to create a shared universe across several different television programs.
In particular, the shared nature of this universe has allowed stories begun on one of the shows to be continued on a different series. In some cases, this has meant that important narrative developments—such as Martha Jones' employment by UNIT (TW: Reset), Sarah Jane's conflict with a Sontaran who survived the Tenth Doctor's battle with them in the early 21st century (SJA: The Last Sontaran), or the majority of Gwen and Ianto's lines in DW: The Stolen Earth—cannot be fully understood by watching just one of the programs in isolation.
In other cases, the implications of a shared universe are more subtle, as when technology, concepts or cultures that debuted on one program are briefly referenced on another. This happens with frequency on The Sarah Jane Adventures. In one instance, for example, the planet Draconia, which had been the major focus of DW: Frontier in Space, was casually mentioned as having a well-developed form of astrology (SJA: Secrets of the Stars). In another, Sarah Jane's initial suggestions of "Alistair" and "Harry" as possible names for Luke in SJA: Invasion of the Bane was a subtle reference to Harry Sullivan and the Brigadier—characters who had, at the time, not even been mentioned by a BBC Wales production. Likewise, Sarah's description of the origins of her coulrophobia in SJA: Day of the Clown returns the viewer to the setting of A Girl's Best Friend. While such "crossovers" are not narratively significant, they nevertheless reinforce the notion of a single, shared universe.
Canon and the Whoniverse
Defining the exact nature of the Whoniverse can be an exercise in determining which events are a part of an accepted canon and which are not. It is often assumed that if an event can definitively be described as having been set in the Whoniverse, then it must, by definition, be canonical. A classic example of this is the film, Dr. Who and the Daleks. Because the universe depicted in that movie does not appear to be the same one as that which was portrayed in the William Hartnell serial, The Daleks, Dr. Who and the Daleks is often judged to be set outside the Whoniverse, and is therefore not canonical. However, in the short story ST: "The Five O'Clock Shadow", the universe of the Dalek movies is described to be a sort of fairy tale that the First Doctor tells to Susan. Thus, while the Dalek movies are not a part of the Whoniverse, some writers have chosen to consider them loosely canonical. Likewise the comic characters of John and Gillian (TVC: "The Klepton Parasites, and others) are not generally regarded as part of the Whoniverse, but they have been made canonical by later writers' efforts to explain them as dreams of the Eighth Doctor (DWM: "The Land of Happy Endings").
Conversely, just because a story is set firmly in the Whoniverse does not mean it is canonical. This can be observed most easily in fan fiction. Amateur efforts generally depend upon the reader believing that they are being told a story that actually happened to the Doctor and his companions. For this reason, fan fiction is often laden with many references to known elements of the Whoniverse. However, a common aim of fan fiction is also to describe an event that would never happen on the television series, such as sexual encounters between improbable partners or attempts to better define exactly who the Doctor is.
Because of these difficulties, many people involved in the BBC Wales production of Doctor Who, shy away from defining what is or is not canon. Steven Moffat observed at the 2008 Comic Con in San Diego that it is "impossible" for a show about a dimension-hopping time traveller to have a canon. The question of whether an event "counts" is less important than whether a particular story feels like it "belongs" to the universe of Doctor Who. In this sense, the creators of Doctor Who professional fiction for BBC Wales seem less concerned about the minutae of canon agreement (does the Sarah Jane of The Sarah Jane Adventures have the same birthday as she gave in a 1974 Doctor Who serial?), and more about creating a plausibly integrated universe (when Sarah Jane met Captain Jack in Journey's End did it feel "right"?).
