I want to open a metaphor for you. A word. Door. With language I can create an opening; on the other side describe, perhaps, a classroom: the space of the room lit with flickering greens or whatever other colors flow from electric screens, the ambiance the humming fans of computers, the cackling of keys. In a MUD I can do that: create a room, or an object, structure it to my liking with my words. I can do that here as well, use my words to create a scene. The disparities between a word world described here and one erected in a social MUD may not be that great. While a MUD is more directly a text-based reality, the reality of this room, this gathering, can depend on the coming together of our language, talk either constructed here through mutual agreement, or mediating our cognitive selves.
This paper has nice words for this very Psybernettic notion.