MediaWiki is a popular free  web-based wiki software application developed by and used on all projects of the Wikimedia Foundation, as well as on many other wiki websites worldwide. It is written in the PHP programming language with a backend database.

The software is optimized for efficient handling of projects of all sizes, including the largest wikis which can have terabytes of content and hundreds of thousands of hits per second.[8]  Because Wikipedia is one of the world's largest websites, achieving scalability through multiple layers of caching and database replication  has also been a major concern for developers. Wikipedia and other Wikimedia projects continue to define a large part of the requirement set for MediaWiki.