The term “fictional world” is sometimes used to describe the "universe" within which a transmedia narrative is set (Dena, 2009, p. 21). The term "storyworld" has also been used to describe that "universe". Dena specifically rejects the use of the term “storyworld” because some transmedia products incorporate game elements that are not narratives (Dena, 2009, p. 23).
Because transmedia narratives can be fiction, non-fiction, or a combination of both, the use of the term “fictional world” could be misleading. Narrative/story is an integral element of a transmedia narrative. Therefore, I will use the term “storyworld” rather than “fictional world”. It also helps that "storyworld" is increasingly being used as the term of choice by professionals in the field (and the recent Storyworld conference further supports the use of the term).
As the term “storyworld” becomes increasingly common in the discussion of transmedia narratives and is an integral part of their definition, I'll use a definition in which a “storyworld” refers to the shared universe within which the settings, characters, objects, events, and actions of one or more narratives exist.
As we dig more deeply into the structure of transmedia narratives, you will see why a solid definition is needed and (hopefully) why I've gone with this one.
(Christy Dena's excellent thesis on transmedia practice can be downloaded from Scribd.com.)
Dena, C. (2009). Transmedia Practice: Theorizing the Practice of Expressing a Fictional World Across Distinct Media and Environments. PhD disseration . Sydney, Australia: University of Sydney.