Referer
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Referer is a common misspelling of the word "referrer"; so common, in fact, that it made it into the official specification of HTTP - the communication protocol of the world wide web. When visiting a webpage, the referer (sic) or referring page is the URL of the previous webpage from which a link was followed. More generally, it is the URL of a previous item which led to this request - the referer for an image, for example, is generally the HTML page on which it is to be displayed. The referer is part of the HTTP request sent by the browser program to the web server.
Many web sites log referers as part of their attempt to track their users. Most web log analysis software can process this information. As referer information can violate privacy, some browsers have the option of disabling this functionality. Some proxy and firewall software will also block referers, to avoid leaking the location of non-public websites. This can in turn cause problems: some servers block parts of their site to browsers that don't send the right referer information, in an attempt to prevent deep linking or unauthorised use of images (bandwidth theft).
Recently many blogs have started publishing referer information in order to link back to people who are linking to them, and hence broaden the conversation. This has led, in turn, to the rise of referer spam. Referer.org is such an example.
Reference
- RFC 2616: Hypertext Transfer Protocol -- HTTP/1.1de:Referer