Whoniverse, a portmanteau of the words "Who" and "universe", is a word used to describe the fictional setting of the television series Doctor Who, Torchwood, and The Sarah Jane Adventures, as well as other related stories. The term is often used to link characters, ideas or items which are seen across multiple productions, such as Sarah Jane Smith from Doctor Who, K-9 and Company and The Sarah Jane Adventures, Jack Harkness from Doctor Who and Torchwood as well as K9 from Doctor Who, K-9 and Company, The Sarah Jane Adventures, and K-9.
Before the expansion of the Doctor Who fictional universe, the term "Whoniverse" referred to everything connected with the programme, both in-universe and behind-the-scenes. In this original meaning, standing exhibitions, discussions about the filming of episodes and even fandom itself were considered part of the "Whoniverse".
Unlike the owners of other science fiction franchises, the BBC takes no position on which Doctor Who stories are definitive for future projects. The show has no 'canon', and indeed, recent producers of the show have expressed distaste for the idea. Though the term is essentially an example of fanspeak, it has recently begun to appear in mainstream press coverage following the popular success of the 2005 Doctor Who revival.
Source: Wikipedia, "Whoniverse", available under the CC-BY-SA License.