TrackBack is a feature of Movable Type that allows you to let other sites know that you have linked to them, and lets you know when other sites have linked to you. The TrackBack feature will place a direct link on your Movable Type entry to entries from other sites that are linking to your entry. Conversely, if you place a link on your weblog entry that links to another site's entry, a link to your site will show up on the other site's entry.