TrackBack (manual) enables weblogs to ping each-other, so if I am writing about something that Mike has already posted about – I can add his trackback url and his posting will be pinged, and I will be listed among the “Trackbacks”. Its a great way to keep track of weblogs posting about the same topic, and adds another layer to the “conversation”, at least IMHO.
Here is what MovableType writes about trackback:
Movable Type’s TrackBack system allows peer-to-peer communication and conversations between weblogs. Imagine that you write about a movie you just saw in an entry on your Movable Type-powered weblog. Another MT weblogger reads your entry, and wants to write an entry referencing your original post. He could just comment on your weblog, but he’d like to keep the post in his own database and host it on his site.
Using TrackBack, the other weblogger can automatically send a ping to your weblog, indicating that he has written an entry referencing your original post. This accomplishes two things:
On your site, you can automatically list all sites that have referenced a particular post, allowing visitors to your site to read the response on the other user’s weblog.
It provides a firm, explicit link between his entry and yours, as opposed to an implicit link (like a referrer log) that depends upon outside action (someone clicking on the link to your entry).
All in all a very cool feature. My blog is configures so that MT will go out and look for Trackback configurations on the pages I link up, and then automatically ping them (Its called TrackBack auto-discovery) – and is a feature that can be turned on and off. It still has its quicks, it won’t look at the URLs you add to ping and the auto-discovery urls – so if you add URLs manually and are running auto-discovery at the same time, you risk pinging other blogs twice. Hopefully something that will be fixed in later implementations.