If you'd like some more background it might help to link to a couple PDF articles:
Immersion, Flow And The Experiences Of Game Players (241k)
stop saying "immersion"! (184k)
Both articles discuss the difficulties of the term "immersion" due to different meanings ascribed to it. I agree with the general thrust of the articles even though I wouldn't necessarily say that either one presents an exhaustive list of observed usages and meanings. What is interesting, though, is that one article concerns video games, while the other concerns RPGs (presumably both LARP and tabletop). I had expected that, due to more attention and peer review in academia, video game articles would actually have a fairly well-established definition of "immersion" even if it didn't correspond well with ideas found in RPG discussion.
From the RPG side, I believe I have a fairly good picture of the sequence of events--although I'd be interested in evidence contrary to my account. Essentially, "immersion" was a well-established and fairly stable term in discussion on rec.games.frp.advocacy in the 1990's, as summarized by John H. Kim here. In fact due to the history of rgfa discourse, as a reaction to the aggressive advocacy of Theatrix by one of the participants, "immersion" was almost certainly conceived, in part, to explain some people's sense that minimizing both "drama-based GMing" and the use of "metagame" knowledge/resources tended to produce a certain experience that was distinct from playing a game that did have those characteristics.
Unfortunately I don't have much first-hand knowledge of roleplaying theory discussion after the mid-90's, especially outside of Usenet. But I believe that what happened was that the term was imported into an entirely new context in rpg.net and other places, but without the rather strong policing from which it had earlier benefitted. (There were both social and technological factors at play, notably the difficulty of participating in Usenet compared to web forums. Also simply the relative age and institutional memories of the two media.) As a result, I speculate that a lot of people heard others talking about "immersion" and without access to the history of the term, they cast about for meanings. From this came multiple hypotheses about what immersion "is", instead of "what are those people talking about?" It's likely that some people picked up the term and made it their own, further confusing things, as even nominal "immersionists" couldn't agree with each other.
But where did the new meanings come from? My thought was that they came from video game theory, and indeed I'll bet that "Flow" first made its appearance there and was then picked up by tabletop theorists rather than being directly imported from the original source (that is, Mihaly Csikszentmihalyi).
However, based on the article by Steven Pace that I linked above, it's clear that the video game field itself suffers from lack of clarity over the meaning of "immersion". This raises several questions:
1. How sure can I be that video game theory is the vector through which "Flow" passed into rpg theory?
2. How many other notions of "immersion" traveled the same route?
3. How did video game theory reach its muddle over "immersion"? I suspect it was a similar process. It's even possible that the rgfa definition filtered into video games. In any case it would be illuminating to trace the agglomeration of meanings over time.
Ultimately what I hope to demonstrate is that none of the meanings of "immersion" is especially difficult or mysterious--they've just been confounded with each other. And second, I suspect that a number of the meanings are actually stabs in the dark by people for whom "immersion" wasn't really a concern.