What is a Wiki?
At the second Wiki symposium, participants were rapidly tiring of the question, "What is a wiki?" That's right on schedule; the second conference always gets tired of these tiresome definitions.
At one extreme, a wiki is a descendant of Ward Cunningham's original wiki. At another extreme, a wiki is a hypertext where readers can also revise and write. Following Michael Joyce, hypertext research has always called this constructive hypertext. In some ways, wikis do epitomize Joyce's vision of constructive hypertext:
versions of what they are becoming, a structure for what does not yet exist
I'd like to propose a middle way, a definition that is broad enough to contain everything that's distinctively wiki-like (though not everything that has some WikiNature in it).
Wikis are constructive hypertexts in which each place has a name, and writing that name represents a link to that place.
Hypertext systems always balance an emphasis on lexia with an emphasis on links. Intermedia and Storyspace foreground the links: you see the Web View or the Storyspace Map before you see the text. Sometimes, it's almost as if the text decorates and extends the structure of connection. The spatial hypertext systems VIKI, VKB, and ART foreground the structure, too, even though they don't have links. ZigZag is close in spirit, too; the structure is Spartan but it's always very close to the surface. NLS/Augment, the Web and most of the OHS implementations are more balanced; there's less emphasis on overt structure but the links are always present (and they're often painted bright blue and underlined just to make sure you notice).
Wiki is the most extreme of place-centered hypertexts. A place is its name, and that name is a token you can always redeem for a trip to that place. This gives Wiki power; it's very easy to create a link. It's easy to make a new place: if you link to a place that doesn't exist, the link brings its destination into existence. It's also easy to imagine the consequences of following a link: unless you build pages with misleading names, the link name stands for its content. Ironic links, as in Victory Garden, are tricky to pull off in a wiki. Feints (see Patterns of Hypertext) don't have WikiNature.