The referrer, or HTTP referrer — also known by the common misspelling referer that occurs as an HTTP header field — identifies, from the point of view of an Internet webpage or resource, the address of the webpage of the resource which links to it. By checking the referrer, the new webpage can see where the request originated.

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The Referer header dates back to the beginning of HTTP and has the dubious honor of being the only header standardized with a misspelt name.