I just learned the difference between a trackback and a pingback: 

A trackback is a small message sent from Site A to Site B to notify Site B that Site A wants to reference a post on Site B and provide a way for Site B to link back to Site A's reference.  That's a very complicated way of saying a pretty simple thing.  There's usually a textbox in the post-writing section of a website to paste trackback links. 

A pingback is the same thing, except that it's done automatically by pasting a link in the post content.  So instead of pasting the trackback link in a separate textbox, the trackback is sent directly from the content textarea.  For example, if the sites referenced above could accept trackbacks, they would receive a trackback from this post because it links to them.