"Wiki" is the overarching name for a cross-linked website that is produced and edited by the community that frequents it. Wikipedia is the most well-known wiki.
Is a collection of wikis, backed by the Wikimedia Foundation. Their mission is to "bring free educational content to the world." For a full list of Wikimedia wikis click here.
MediaWiki is the open-source platform built by the Wikimedia Foundation in 2002. It powers every WikiTeq and Wikimedia project, including Wikipedia.