What is link popularity?

From Wikipedia:
Link popularity is a measure of the quantity and quality of other web sites that link to a specific site on the World Wide Web. It is an example of the move by search engines towards off-the-page-criteria to determine quality content. In theory, off-the-page-criteria adds the aspect of impartiality to search engine rankings.

Link popularity plays an important role in the visibility of a web site among the top of the search results. Indeed, some search engines require at least one or more links coming to a web site, otherwise they will drop it from their index.

Search engines such as Google use a special link analysis system to rank web pages. Citations from other WWW authors help to define a site's reputation. The philosophy of link popularity is that important sites will attract many links. Content-poor sites will have difficulty attracting any links. Link popularity assumes that not all incoming links are equal, as an inbound link from a major directory carries more weight than an inbound link from an obscure personal home page. In other words, the quality of incoming links counts more than sheer numbers of them.

NOTE:  Google's latest ranking algorithm, called Jagger, decreases the significance of link popularity, favoring content quality instead.

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