Backlink
Backlinks are incoming links to a website or web log. The number of backlinks is an indication of the popularity or importance of that website.
Search engines often use the number of backlinks that a website has as one of the factors for determining that website's search engine ranking. For example, Google's PageRank algorithm uses backlinks to help determine a site's rank. To see a site's PageRank, you need to use the Google Toolbar for Microsoft's Internet Explorer, view the bar graph indicating a website's PageRank in Google's website directory, or download the PageRank plugin for Mozilla Firefox.
You can determine the approximate number of backlinks a website has when doing a search at Google by adding "link:" before the website's URL. For example, here is the Google search for "wikipedia.org": [1].
See also: Google bomb