XFN (XHTML Friends Network)

XFN (XHTML Friends Network) is a microformat developed in the early days of the web to represent human relationships through hyperlinks. By adding simple attributes like rel="friend" or rel="colleague" to links, web creators could indicate their relationship with the person behind the linked site.

It was an early step toward social networking—helping machines understand the social connections between people online before platforms like Facebook or LinkedIn existed. While largely outdated today, XFN played a foundational role in the development of web-based identity and social graphs.