Trackback is a means of notifying a website that another website has linked to it. By linking to a trackback link, a webmaster can automatically inform the other website that he has added a link to one of site's pages. However, in order for the trackback system to work, both websites must support trackback. This is because the linking website needs to ping the linked website to let it know a link has been added.
Trackback was first implemented by Movable Type blogging and Web design software in 2002. Since then, other Web development tools, such as Wordpress and Typo, have also added trackback support. This allows bloggers from all types of platforms to communicate with each other. For example, a user might read a blog entry on another person's site and decide to post his own blog, responding to the original post. If he adds a trackback link, the original blogger will see that the other user has linked to his blog. Depending on the trackback settings, the new blog may also show up as a link at the end of the original blog.
Since trackback requires multiple websites to support the trackback protocol, it continues to be used primarily for blogs. However, some news websites now offer trackback links as well. You can tell if a site supports trackback if there is a "Trackback link" or "Trackback URL" at the end of an article. Sometimes the link will be followed by a number, which indicates the number trackbacks that link back to the blog.