Referrer

Definition: A web page, containing a link to your web page, that delivered your visitor to your web page. For example, if Google’s search results (for example on a search for “Britney Spears”) contained a link to a page on your site and the user clicked on that link.

FirstClickSEO Commentary: This is how we can determine what search phrase someone used to get to your Web site. Or which Web site sent the visitor to your site.