[<< wikibooks] MediaWiki Administrator's Handbook/Editing in the MediaWiki Namespace
Editing pages in the MediaWiki namespace is one of the more complicated and serious abilities of an administrator, and must be undertaken with extreme caution because it can change the appearance of the entire website. 

MediaWiki:Uploadtext – Text appearing on the upload page, including warnings about images without copyright information, etc.
MediaWiki:Sitenotice – Text that appears at the top of every page on the site, just below the tabs
MediaWiki:Copyrightwarning2 – The copyright warning that appears below the edit window.
MediaWiki:Common.css – Style sheet (CSS) defining site appearance, common to all skins
MediaWiki:Monobook.js – Contains scripts in JavaScript
MediaWiki:Edittools – Provides list of special characters appearing below edit box and save/preview buttons
MediaWiki:Sidebar – Defines 'navigation' box in top-left corner, and allows for the creation of other navigation boxes (such as the 'community' box on wikibooks)
MediaWiki:Revertpage – Text added to the edit summary when using the rollback tool.
MediaWiki:Monobook.css – Style sheet (CSS) defining site appearance in default skin.
MediaWiki:Licenses – List of available licenses for images/files appearing in a drop-down list on file upload page.
MediaWiki:Sharedupload – Appears on the page of any image or file used in wikibooks but actually located on commons. Most wikis use a template linking to the commons page.
MediaWiki:Tagline – The text appearing just below a page title (on wikibooks, this currently reads "From Wikibooks, the open-content textbooks collection").