trackbacks: is linking to a post that you like or has relevant information about your post. it is "track"ing "back" to the original post eithere where you got the idea or you expand about the idea.
it then rewrites a snippet of that post to the originals post you linked to as a comment.
TrackBack is most commonly used by manually copying the TrackBack URL of an existing page and pasting it on a new page. Pages that support TrackBack include a TrackBack URL that can handle pings (e.g. http://somewhere.blog/trackback/demo-post).