Wiki
A wiki is a web page able to be contributed to and edited by many users, as such it is a collaborative system. An interesting article on the background of how a wiki works can be found at http://computer.howstuffworks.com/wiki.htm.
Edit Wars
When people create or modify an article, they can become quite possessive about the content, and when an article is edited, previous contributors/creators can be automatically alerted to any changes, and have the option of "reverting" the article to a previous version. This can set up what is known as an edit war (or revert war), where an article is repeatedly edited/reverted between two versions.
There is an amusing subsection on edit wars here, with a link through to a Wikipedia article on "Lame edit wars".
One example of notable relevance to New Zealanders is a long running edit war on the origins of the pavlova: "which was invented in Australia 4, New Zealand 5, Australia 6, 7, 8, New Zealand 9"