Synthetic immersive environment
A synthetic immersive environment could be used synonymously with the term "metaverse", or "virtual reality": a simulated, artificial, digital environment that allows users/players to "lose" (i.e., immerse) themselves in it.
There are many reasons for which "virtual reality" is not desirable. For example, in some cases we actually want to create an environment that is "hyper real". In fact, one could argue that no synthetic environments, by the nature of their existence, are really "real" to be referred to as such.