referrer - Computer Definition
The URL of the Web page a request is coming from. When you click on a link to go to another page, or when the Web page itself calls for an image to be displayed, the browser sends the URL of the current Web page along with the request. On a search site, in addition to the URL, the text you are searching for is often sent to an advertising agency that sends back a tailored banner ad or just collects demographics. Most ad blocker programs can eliminate referrer data. See ad blocker.