Microformats

Thus microformats are developed in line with “plain old semantic HTML” (POSH) practices and principles, that is, as valid semantic extensions to HTML. Semantic HTML by itself enables sharing open content with headings, paragraphs, and lists, etc. Microformats build upon that foundation, reusing rather than reinventing (i.e. XOXO reuses HTML for lists and nested lists for outlines, rather than inventing new tags or vocabulary), and extending only for commonly published semantics beyond HTML, such as contact information, events, reviews, episodic content, etc.

Here: http://microformats.org/