The system watches for a visitor to arrive at your site or at a specific page on the site by clicking a link from a site or page with given attributes (for example, a specific URL).
Examples:
Is referred by external site where referrerURL is http://www.example.com/products/shoes.jsp
Is referred by external site where referrerSite is www.example.com
Is referred by external site where referrerPage is /products/shoes.jsp
Note that this event can be used to track arrivals both from external sites and from pages within your own Web site.