The web browser that the user used to access the URL, for example, Internet Explorer. This information is sent in the HTTP request to the server.
The URL of the web page that linked the user to another web page; it is the source that redirected (referred) the user to the web page that is being requested.
The option in the HTTP request header field that preserves the IP address of the user who requested the web page. If you have a proxy server on your network, the XFF allows you to identify the IP address of the user who requested the content, instead of only recording the proxy server’s IP address as source IP address that requested the web page.