This article is excerpted from Designing Virtual Worlds by Richard A. Bartle (New Riders Publishing, 2003, ISBN 0-7357-1351-0).
In this context, a world is an environment that its inhabitants regard as being self-contained. It doesn't have to mean an entire planet: It's used in the same sense as "the Roman world" or "the world of high finance."
So what about the virtual part? Not to get too philosophical about it:
Real. That which is.
Imaginary. That which isn't.
Virtual. That which isn't, having the form or effect of that which is.
Virtual worlds are places where the imaginary meets the real.
A computer implements virtual worlds (or network of computers) that simulate an environment. Somebut not all of the entities in this environment act under the direct control of individual people. Because several such people can affect the same environment simultaneously, the world is said to be shared or multi-user. The environment continues to exist and develop internally (at least to some degree) even when there are no people interacting with it; this means it is persistent.
Although virtual worlds now have many applications beyond that of being mere entertainment products, they began as computer games; furthermoreperhaps because of the large sums of money involved in their creation and the guaranteed huge monthly incomes they can generatecomputer games remain at the cutting edge of virtual world development.
For these reasons, much of the vocabulary commonly used to describe virtual worlds is games-based. Thus, the human beings who interact with the simulated environment are known as players rather than users; the means by which the environment introduces goals for the players is called gameplay; the activity of interacting with the environment is referred to as playing.
Specialists may adopt a different vocabulary that is formal for their particular area of expertise, for example a cultural anthropologist might prefer to talk of "individuals" exhibiting "behaviors" in response to "pressures;" however, for any broader discussion of the subject the dominance of game-oriented terminology is impossible to resist, and it is therefore the one that shall be used here.
The exception is the very term "virtual world" itself. Over the years, a number of words, phrases, and contrived acronyms have been used to describe these projected milieux, none of which have been entirely successful. Virtual worlds were originally known as multi-user dungeons (MUDs). The "D" in MUD stands for "Dungeon." Contrary to what many people assume, this has nothing to do with the role-playing game Dungeons & Dragons and does not mean that the game world had a dungeon setting. Instead, it is because the version of a single player game called ZORK that Roy Trubshaw (one of the author's of MUD) played was a Fortran port called DUNGEN. (The DEC-10 used six-character, all uppercase filenames. This is why "Dungeon" is referred to as DUNGEN and "Adventure" as ADVENT by old-time hackers like me.) Roy wanted something that was like a multi-user DUNGE(o)N, and the acronym MUD immediately presented itself.
Although this term is still in common currency to the extent that it has made it into several regular dictionaries, it is not universally accepted. In particular, many players of certain of its subcategories see it as implying some kind of combat-oriented world view, and prefer the term MU* instead (MU for multi-user and * for anything that could conceivably follow).
This would be analogous to calling dinosaurs *saurs on the grounds that "dinosaurs" vaguely implies that they were all pea-brained carnivorous monsters, whereas in fact many were pea-brained herbivorous monstersand hey, there are pterosaurs and plesiosaurs, too. ("Dino" comes via New Latin from the Greek deinos, meaning "fearful." Saurus merely means "lizard.")
The first virtual worlds were text-based, in that their environments and the events occurring within them were described using words rather than images. Confusingly, although the term MUD applies to virtual worlds in general, the term MU* does notit's used strictly for text-based worlds. The introduction of computer graphics into the mix therefore caused a second spate of naming, in order to make a distinction between graphical MUDs and text MUDs. At first the new games were called persistent worlds, but when the enormous numbers of simultaneous players they were attracting became their defining feature this changed to MMORPGs (massively-multiplayer online role-playing games). Said acronym dominates at present, but it is rarely used with enthusiasm (not least because it's unpronounceable) and it is therefore likely to be abandoned the instant some viable alternative emerges.
Although, properly, all these persistent, shared, computer-moderated environments can and should be referred to as MUDs, the term is sufficiently loaded that outside the cognoscenti it is unlikely to be universally interpreted this way. Enough people think that MUDs are a mere category of MU*s (rather than the reverse) for it to be confusing. Therefore, this article prefers the more descriptive and less emotive "virtual worlds" as an alternative.
It is important to note that virtual worlds are not the same as virtual reality (VR), which has a much more specific meaning. Virtual reality is primarily concerned with the mechanisms by which human beings can interact with computer simulations; it is not especially bothered by the nature of the simulations themselves. People who visit virtual worlds may some day benefit from research into visors, data gloves, and beyond, but the fundamental attraction for them is what awaits when they enter a virtual world, not the means by which they do so.