What is Microdata and Microformats?

You don't want to surround all your content in DATA tags because it's not all data. That's where microformats come in. Microformats help you define the content of your pages as specific things beyond just data and let that information be machine-readble as well.


Microdata is a set of human-readable libraries added to HTML to make that HTML more semantic, and thus more computer-readable as well. You use microdata with existing HTML tags and attributes to define data that computers can use and humans can read. 


For example, an event that is marked up using microdata can then be added to a reader’s calendar without the reader needing to type in any of the event data. Instead, they would simply click a link and the event would be automatically added to their calendar including the start and end times, location, and any other information that is marked up with microformats.


Microformats use existing HTML attributes and elements like class, rel, and SPAN to define the microdata.


http://webdesign.about.com/od/microdata/a/what-is-microdata.htm?nl=1