What Is MediaWiki?
From MediaWiki Beginners Wiki
MediaWiki is what's called "wiki software", a type of program that lets a community of internet users submit content that is editable online via a web browser, such as Internet Explorer or Mozilla FireFox. It was invented by the Wikimedia Foundation for their wiki projects, such as Wikipedia, Wikimedia Commons, and MediaWiki.org, and is freely available for download for public and private use.
It's primarily meant to be used for the very purpose it is used for on Wikipedia, which is to make the world's largest online encyclopedia, but MediaWiki is completely free software that can be modified to do almost anything that it's users wish it to do, with their only limits being their skill in using and modifying the software.
However, most people who use MediaWiki probably don't have any grand ideas about tinkering with the codebase of the software to make it do wild and crazy things. Most people don't even run the software, they just go to websites running it, sign up as users, and add content, letting the people who run the site worry about the fine details.
That said, this wiki is aimed at those who DO have have to worry about the fine details, or to be more exact, people who've just gotten a copy of MediaWiki on a web server or a localhost (private, not connected to the internet proper) install and aren't sure what they are doing.
Some may get as far as setting it up, then be like "Okay, now what do I do?". Some may get to the installation screen and not know what settings they need to pick. Some may be lucky enough to set it up, get to the actual wiki, do some basic editing, but have no idea what extensions and templates and wiki words and parser hooks and so on mean.
If that's the case, this wiki is going to (hopefully) help clear up some of the confusion, explain all this complicated business in simple to understand language, and (again, hopefully) point beginners in MediaWiki in the right direction.