inside the world of the narrative. This and its contrary term extradiegetic are usually used in reference to the narrator and the narratee, but not necessarily exclusively.
If a space itself, or a series of objects and/or inscriptions within it, is identified by the narratee as telling the story then we can say that the narrator is intradiegetic.
In a more complicated formulation, in a museum a curatorial voice is typically intradiegetic to (inside) the diegesis of the museum itself (but not necessarily narrating the story of the museum, though it could be), but extradiegetic to (outside, telling) the diegesis of the collection or exhibition it is ‘talking’ (sometimes really talking) about.
the narratee can be drawn into the story (intradiegetic narratee) through metalepsis, to become a participant in the world of the story, even to be the protagonist, as is often the case in gaming. In narrative environment design this can be a very powerful tool indeed but needs to be used with discretion, as the intense emotional engagement that it can engender has to be handled with care. See metalepsis.
Broader terms:The diegesis