Yes, it is the referer header, for example this is what my browser sends when clicking a link from Bing after searching for google: Referer: https://www.bing.c

Yes, it is the referer header, for example this is what my browser sends when clicking a link from Bing after searching for google: Referer: https://www.bing.com/search?q=google&pq&cvid=3C49B41400954D399CEF88966B13xxxx https://www.bing.com/search?q=google&pq&cvid=3C49B41400954D3... Google can use that to see your search terms because it in the value of the q attribute. If they don't go to a Google property then they will still be able to get this information, if the website they do go to uses Google Analytics (which is most of the web).