MediaWiki is a wiki application written in PHP that the Wikimedia Foundation developed to run several of their projects. The encyclopedia Wikipedia is the most popular of these projects.
A wiki is a type of website that allows its users to create and edit content in a collaborative manner. It can be used in several ways, including as a knowledge base, documentation library, community website, or company intranet.
These kinds of websites are especially useful in contexts where several people need to create and modify pages in a quick and easy way.