A wiki is a website that allows many people to edit its content. It is a much different paradigm from the old days of static pages created by single people. Having more than one person editing creates a need to have a type of system to moderate edits and provide methods for seeing who edited what and keeping track of useful metadata for pages.
When I found Wikipedia, I was was very impressed with wikis and their possibilities, so I decided to make my own parser for wikicode which quickly acquired a page history system, then later a user privilege system, and ultimately the entire KyleWiki3 software. KyleWiki3 is the third version of KyleWiki after two major overhauls from the inital versions. The software, somewhat surprisingly, isn't entirely wiki-specific, and I've had much success using large chunks of code for other projects such as an online image storage and retrieval system.