My three or four readers may be wondering what the TrackBack link at the bottom of each post is for. It’s where you’d normally expect a link to leave a comment — Karen Traviss wanted to leave a comment thanking me for this post, and discovered that that’s not what the TrackBack link was for. So it occurred to me to try and write a brief primer.

TrackBack is a remote commenting system. Let’s say Reader A reads a blog post by Blogger B. Instead of leaving a comment on B’s post, A goes to her own blog and writes an entry that links to B’s entry. A’s blogging software goes through her entry, finds the link to B’s entry, and figures out where to send a TrackBack ping. Sends the ping to B’s server. B’s blogging software receives the ping, which contains an excerpt from and link to A’s blog entry. Depending on how B has configured her blog, that excerpt and link might appear beneath B’s entry. Essentially, A’s blog is telling B’s blog that A is writing about B, and B’s blog makes a note of it. It’s a way of tracking debates or conversations over many web sites: “These people have linked to this entry, and may have something more to say on this subject.”

These TrackBack tutorials do a much better job of explaining it:

• Movable Type: A Beginner’s Guide to TrackBack
• How TrackBack Works
• What Is TrackBack?

Does that help? It’s worth noting that not every blogging tool supports TrackBack. Movable Type does — hell, they invented it — but Blogger and LiveJournal don’t. (So, for example, Karen Traviss couldn’t send a TrackBack ping from her blog.) But now that the company behind Movable Type has acquired LiveJournal — and, if you want to see TrackBack in action, see how many there are for that post! — who knows?