Manual:$wgSitename

Details
The name of the site, as displayed throughout the site. Should always be changed from its default value. During setup, this setting should be provided on the initial setup screen, and the value provided is included in LocalSettings.php once the setup process is completed successfully.

This name gets included many times throughout the system. For instance, the Wikipedia tagline "'From Wikipedia, the free encyclopedia."' makes use of this setting. It is mainly used through the magic word " ".

If $wgMetaNamespace is not set, it will be automatically initialized to this value. Make sure the name is appropriately formatted: valid title characters, etc.