Glossary
Referrer
The page a visitor came from, as reported by their browser in the Referer header, when it reports one at all.
The header is famously misspelled in the HTTP specification, which is why code says Referer and prose says referrer. It is sent by the browser rather than by the site, which means the site being linked to has no control over whether it arrives.
It is missing far more often than people expect. A link opened inside a native app usually sends nothing. Most sites now send a Referrer-Policy of strict-origin-when-cross-origin, which gives the domain and never the path. Anything typed, pasted or scanned from a QR code has no referring page by definition.
This is why analytics screens show a large bucket called Direct. Direct is not a traffic source. It is the absence of one, and reading it as "people who came straight to us" is the single most common misreading of a link dashboard.
