Oasis or Wikia is one of the two available skins on Wikia, and the standard skin one views a wiki in. You can check out what it looks like by attaching ?useskin=oasis or ?useskin=wikia to the end of your URL or changing to Oasis as standard skin in Special:Preferences. The latter method is only available for registered users, but unregistered visitors of the site will see a Wikia wiki in Oasis by default.