A wiki can be defined as a collection of informational nodes that are often editable by everyone, deeply cross-referenced with links, and usually use a simple text markup language that is converted to HTML by the wiki software. The first wiki to call itself Wiki, was Cunningham and Cunningham's C2 Wiki. Originally intended for use by the Portland Pattern Repository, a user group in Portland, Oregon, C2 rapidly grew to be an impromptu encyclopedia of useful concepts for developers because of how easy it was to add to the information presented there. Other wikis, from the mighty and awe-inspiring Wikipedia to our own humble little manual server, can generally claim a spiritual ancestry from C2, which still thrives today.
Content served by a wiki is broken down into nodes. A node is associated with a single topic, and has a title that serves as its address in the wiki, and content that contains the actual text of the node. The content, which you are reading right now in the "Browsing Nodes" node, can contain a myriad of typographical constructs but can be simply expressed as some text, interspersed with links to other nodes, to nodes that have not yet been created, and to Internet resources outside of the wiki.
Probably the greatest feature of wikis that escapes the notice of a new user is the references interface. By clicking on the Node References link in the command bar at the right, you can quickly see all the other nodes in the wiki that refer to the one you are perusing. By looking at nodes that refer to a node you are reading, you can often quickly find other information in the same vein. Wikis often use this backwards referencing to build hasty indexes of related material, in a practice known as tagging.
For example, at the bottom of this page, you can see a line that probable looks like the following:
This node is a part of the {cloud wiki manual}, and still {needs revision}.
This serves many purposes. The "cloud wiki manual" tag tells you where you could find the table of contents for the wiki manual, it tells authors to be careful when editing this page, and it ensures that this node will show up in a list of references to the manual, allowing the manual node to be used as a kind of index to everything about the manual.
The "needs revision" tag indicates that this node could use some editing by someone who knows the topic. Some nodes never lose this tag, simply because they are so crucial that they deserve constant attention. This is often called a maintenance tag, and is a good example of how tagging can be used to quickly find pertinent nodes.
Now, go back to the front page, and start browsing. Make sure you pay attention to the back references, and you should very quickly find your way back to the manual.
This node is a part of the cloud wiki manual, and still needs revision.