A referrer is the URL of the page from which a user accesses another page. For example, if you have two pages,example.com/page1.html and example.com/page2.html, and someone accesses example.com/page2.html from a link on example.com/page1.html, the referrer would be example.com/page1.html. The referrer URL is sent by most browsers as part of a request for a page. If a user makes a direct request for a page (for example, typing example.com/page2.html into the address bar), there will be no referrer information sent.