These topics arose on one chat session. I found very difficult to understand them because I thought they were more complicated but in fact, they are very, very simple...

"Pingback is a method for web authors to request notification when somebody links to one of their documents. Typically, web publishing software will automatically inform the relevant parties on behalf of the user, allowing for the possibility of automatically creating links to referring documents.
For example, Alice writes an interesting article on her Web log. Bob then reads this article and comments about it, linking back to Alice's original post. Using pingback, Bob's software can automatically notify Alice that her post has been linked to, and Alice's software can then include this information on her site."
(from: http://www.hixie.ch/specs/pingback/pingback)