Backlinks from reliable and authoritative websites are one of the important ranking factors. However, in addition to the number of backlinks a website gets, the number of different domains from which the website has backlinks is also very important. Referring domain is the value showing the number of various domains from which a website has backlinks. In order to have a functional backlink portfolio, the number of referring domains and backlinks should not significantly differ. In other words, getting too many backlinks from one website is not recommended by Google, as it will not be organic.