I find XFN (XHTML Friends Network) via Tantek.  What it is...

XFN outlines the relationships between individuals by defining a small set of values that describe personal relationships. In HTML and XHTML documents, these are given as values for the rel attribute on a hyperlink. XFN allows authors to indicate which of the weblogs they read belong to friends, whom they've physically met, and other personal relationships. Using XFN values, which can be listed in any order, people can humanize their blogrolls and links pages, both of which have become a common feature of weblogs.