referrerer

Referrerer is not a standard term in web technology. It is occasionally encountered as a misspelling or informal variant of referer or referrer. In technical contexts, the intended concept is the referer (also spelled referrer in English), which refers to the address of the previous resource that linked to or redirected to the current one.

In HTTP, the header commonly known as the Referer header carries the URL of the page that linked to the requested resource. The header name is Referer, a historic misspelling that has been retained by the specification. The noun form referrer (or referrer) is the standard English term for the source or source page.

Web analytics, servers, and analytics tools use referer data to attribute visits, measure traffic sources, and understand user navigation paths. Privacy concerns and browser policies have led to partial or complete suppression of referer data in some cases. Modern browsers offer Referer-Policy and related controls to limit or customize what information is sent with requests when navigating from one site to another. Common modes include no-referrer, origin, origin-when-cross-origin, and strict-origin variants.

Because of spelling variations, you may see 'referrer', 'referer', or rare informal forms such as 'referrerer' in documentation or discussions. However, the formal HTTP concept remains the Referer header and its related policies. When discussing web traffic sources, it is clearer to refer to the referer (the referring URL) rather than to the nonstandard 'referrerer'.