Nofollow
From The WB7TJD Wiki
MediaWiki-powered wikis often use the nofollow instruction to search engine spiders to prevent spam sites from being added to a publicly-edited article and those sites gaining rank in search results because of the link.
We use the nofollow instruction here by default, but we use an alternative means to linking to outside sites that we have reasonable faith in to not be spam sites, and therefore, their links are followed by search spiders visiting this site.