A way for other blogs to let you know they're using your articles. Like a footnote, but in reverse. It is considered polite to provide a link and a trackback to any articles you reference.
Trackbacks can also be used for spam. It's annoying, but true. See Disabling Trackbacks [1] and Removing Trackback Links [2] for more information.
URL of this document:
http://www.s9y.org/215.html
Links:
[1] http://www.s9y.org/216.html
[2] http://www.s9y.org/214.html