Wikis, otherwise known as Minoteaurlikes, are a kind of software for (metaphysically, excluding wikis which allow handwriting) writing down information to retrieve in the future (note-taking). Specifically, wikis derive from early casual, multi-user, web-based collaborative knowledgebases. Modern "wikis" are often single-user and not web-based, but share the same basic idea of making it easy to create links.
For more information please reread.