Manual:$wgUseTrackbacks

Details
$wgUseTrackbacks enables trackback support if set to true in LocalSettings.php. When MediaWiki receives a trackback ping, a box will show up at the bottom of the article containing a link to the originating page. The link format can be customized by editing MediaWiki:Trackbackexcerpt.

However, MediaWiki does not support sending trackback pings.

Introduction
$wgUseTrackbacks was introduced in revision 10252 (23 July 2005), released in MediaWiki 1.4.8.