Referer spoofing involves modifying the HTTP referer header to disguise the originating webpage. It is commonly used for testing websites and observing their behavior under different conditions. While referer data is not a secure authentication method, some sites still rely on it to control access. Spoofing allows bypassing such referer checks by making a request appear to come from an allowed referrer. Various browser extensions and proxy servers can be used to spoof referrers.