Wiki is web server software that allows users to contribute content. Collaboration is key to Wiki, which is designed as a powerful system for online communities to build web pages and web sites. Unlike blogs and forums, all users are allowed to contribute and edit existing content. Wiki is derived from Hawaiian term "wiki wiki" meaning "quick". The concept behind a Wiki is that collaboration on projects will move it along quicker.
Wikis generally allow web pages to be written, edited and created collectively in a web browser. Wiki supports hyperlinks and simple text. Most Wikis are open, and allow any user ability to edit contents of a Wiki web page. While some say this opens concept to abuse, Wiki moderators and self-policing in Wiki sector appear to be taking hold. Wiki supporters generally feel that it is generally easier to correct mistakes than create content from scratch. Wikipedia is a standing symbol of what many would consider a succesful Wiki.
Wikipedia - Wikipedia is a popular content encyclopedia that anyone can edit. http://www.wikipedia.com
Other topic-specific Wikis like Robin Good's RSS Wiki are proving that collaborative efforts in niche markets can work.
RSS Wiki - http://www.masternewmedia.org/reports/newsmasterstoolkit/wiki/index.php/Main_Page
It is true that Wikis are open to abuse, but by design, it is very easy for a Wiki moderator or other editor to revert Wiki to how it appeared prior to edits, essentially rolling back Wiki and removing any content deemed inappropriate or unrelated. Many Wikis track IP address of visitors and editors, making it easy to track changes and roll back any edits from individuals that appear to be abusing their privileges. In rare cases Wiki operators can protect pages, making them read-only, which restricts any edits from occurring. While such actions are against true Wiki philosophy, restrictions can be used to preserve structure of fully-developed Wikis and protect pages from abuse.