Referer

The Referer HTTP request header contains the absolute or partial address from which a resource has been requested. The Referer header allows a server to identify referring pages that people are visiting from or where requested resources are being used. This data can be used for analytics, logging, optimized caching, and more.

When you click a link, the Referer contains the address of the page that includes the link. When you make resource requests to another domain, the Referer contains the address of the page that uses the requested resource.

The Referer header can contain an origin, path, and querystring, and may not contain URL fragments (i.e. #section) or username:password information. The request's referrer policy defines the data that can be included. See Referrer-Policy for more information and examples.