In terms of SEO, is called referrer ,the URL address of a website which refers the user to another site via a link and which therefore generates traffic on this second site.
In other words, the referrer site includes a link that returns to a page of the target site and on which Internet users visiting this referrer will land by clicking on the link.

Placed on a site that can be considered as a partner, a referrer URL is used to inform the visitor that there is an open door to available resources who are able to provide them with the answers to their question or more information on the subject that interests him. The establishment of this link can be agreed between the two sites or a unilateral decision taken by the owner of the referring site.
In the first case, it can be justified by an advertising exchange agreement, reciprocal services possibly remunerated, and in the second case, the goal can be to direct the Internet user towards a more talkative site or more expert on a subject. that he cannot or does not want to develop too much on his own page.
The word referrer is used on the side of the beneficiary site since it designates the site that brings traffic, the site from which Internet users come via the open door that is the inbound link.
As a qualifier, this word applies sometimes to the page which contains the link, sometimes to the site which includes the page in question.
The acquisition of referrers is done as part of a netlinking during the implementation of a positioning strategy of a site on search engines.

It is the web analytics tools like Google Analytics and associated that determine the referrers on the basis of the information provided by the IP protocol, that is to say by the HTTP server about a visitor who arrives from a URL distant.
This server, which is that of the beneficiary site, receives information including the URL referrer in the HTTP header.
Therefore, he knows who is sending him traffic and can determine the volume as well as the average duration of the site visits.
A dashboard developed by the web analytics tool and showing the structure of traffic coming from referrers will be made available to the webmaster to allow him the necessary analyzes for his positioning strategy. The greatest benefit of this in terms of analysis for the beneficiary website is to know by this means the keywords most entered by Internet users in search engines to arrive on its pages. This will guide his webmaster in optimizing his SEO. This one will also have the possibility of making a sort on the referrers in order to authorize only certain of them.
The limit of the possibilities of analysis is determined by the fact that there are devices on certain browsers and firewalls allowing referrers not to reveal themselves in order to ensure their privacy.
It should be noted however that the pages resulting from direct searches made by Internet users on the engines are likened to referrers too.

Resulting from the Majestic SEO tool, Trust Flow is an indicator used to assess the quality of backlinks to a site or a web page.
It is studied in conjunction with the Citation Flow indicator which, in turn, is used to assess the quantity of backlinks.
The TrustFlow is a numeric value ranging from 0 to 100.

Search engines rate pages and websites on the basis of their trust in reliable content. What better way to do this than analyzing inbound links (backlinks) since their quality and number speak for the trust that other sites place in a given site? It's good to have inbound links to your site, but there is quantity and quality. The quantity of backlinks speaks for the popularity of a site and it is the Citation Flow (CF) tool that measures it.
The quality of the backlinks speaks in favor of its level of confidence and it is the Tust Flow (TF) tool that evaluates it. These two tools are indicators, Flow Metrics provided by Majestic SEO. To find out the values ​​they deliver about a site, including the TrustFlow score in particular , all you have to do is copy the url of this site and paste it into the input field provided for this purpose on the MAJESTIC site. These values ​​serve as the basis for the development of a Netlinking strategy within the framework of natural referencing. They are between 0 and 100. Higher than 40, the TF score is considered high by Majestic SEO. Moreover, since the disappearance of the Google PageRank tool, the TF is used as a criterion to determine the market value of a domain name.

Netlinking has a very important part in an SEO strategy and the mistake is to rely more on the quantity of inbound links than on their quality.
A large number of backlinks can hide a large number of low quality links, which is detrimental to the positioning of the site.
Google Penguin indeed watches over and penalizes poor quality links.
On the other hand, a site with few backlinks but of good quality is recommended by Google and is therefore more likely to appear at the top of the first page of search results for a given query.
Fortunately, the two indicators CF and TF provide the interpretable elements that the developer needs to identify the sources of links to keep and those to avoid.
The backlink providers to keep are those with high TF as well and those to avoid are the spammy or poor quality sites from an SEO point of view.
Since TF is transmissible, they should even be eliminated.
The result of the selections that the developer will make should be such that
their site's TrustFlow score
is higher than the CF score or about the same.
It should be noted that NoFollow links do not transmit the Trust Flow of a page.