All types of traffic to a web site are identified by where the visitor was before they arrived at your web site. When a person clicks on a link on a web site and arrives at another web site this is called a referral.

The site that the person clicks through from is called the referring site. Web analytics packages used to help you understand who is visiting your web site can tell you the addresses of the pages on other web sites that have referred visitors to your web site.

This can be useful for tracking the success of promotions and advertising.