The search engines look very favorably on websites that have an incoming link from a prominent website, where that website does not link back to the other site (This is not surprisingly called a one way link). It’s also known more commonly as a backlink. The search engines as a rule give less importance to a website involved in two way linking (where both websites link to each other) since this has been abused so much in the past by webmasters seeking to achieve high search engine rankings.