Manual:Tagline (Site Subtitle)

Changing the tagline
A way to change the tagline that appears on top of every page just below the page title (but by default is hidden in Monobook and Vector skins except when printing pages) is to modify the MediaWiki:Tagline system message that if undefined defaults to.

Add the following to MediaWiki:Common.css if you want the tagline to display in all skins, or to MediaWiki:Monobook.css if you want to adjust only the Monobook skin:

If you don't like the way it looks (the HTML displaying the text is H3 that displays bold by default in most browsers) add some CSS style declarations to that, eg: