XFN - XHTML Friends Network
From XFN's WEBSITE:
"XFN™ (XHTML Friends Network) is a simple way to represent human relationships using hyperlinks. In recent years, blogs and blogrolls have become the fastest growing area of the Web. XFN enables web authors to indicate their relationship(s) to the people in their blogrolls simply by adding a 'rel' attribute to their tags, e.g....."