noreferrer
noreferrer is a link attribute, rel="noreferrer", that stops the browser telling the next site which page the visitor came from.
noreferrer is a value you add to a link, rel="noreferrer", so the browser doesn't tell the site you link to where the visitor came from. Normally, when someone clicks a link, the browser passes on where they came from, called the referrer. Across sites, that's usually just the address of the site. With noreferrer, it passes nothing.
That makes it a privacy setting for the site that adds it, and a gap in the analytics of the site that receives the visit.
What it does to your analytics
Analytics tools sort visits by where they came from, and the referrer is how they know. A visit with no referrer usually lands in "direct," the same bucket as someone typing your address.
For example, say an online magazine links to Fernhill Coffee's subscription page with rel="noreferrer". The article sends 400 visitors in a week. In Fernhill's analytics, they show up as 400 extra direct visits, and the magazine gets no credit.
noreferrer also does what noopener does, so many sites add it to every link that opens in a new tab. Mozilla's page on noreferrer explains both. Search engines don't treat these links any differently for rankings.
noreferrer and AI traffic
The same gap affects visits from AI assistants. When a person clicks a link in an AI answer, your analytics can only tell it came from ChatGPT or Perplexity if a referrer arrives with it. Links clicked inside apps, copied into a browser or stripped of their referrer show up as direct. That makes it easy to count too few AI visits.
Look for tags on the link too, like utm_source, which survive where the referrer doesn't. Check both when you count AI visits.
In AnswerOrbit
The AI traffic tab in Website shows the visits Google Analytics put down to AI assistants, by assistant, landing page, country and device. Google Analytics can only put a visit down to an assistant when something tells it where the visit came from, so treat the number as a floor.