Microformats provide a way for programs to read certain information in web pages without making the pages look any different to humans. They add semantics to the generic HTML markup in order for these programs to understand the meaning of specific parts of a web page content which is better recognized by humans. For example, a web page displaying a user's profile could use microformats to make it easy for a program to extract the user's contact information so that it can be added to an address book in a single operation. In WordPress, some themes and plugins support some microformats.

Reference http://codex.wordpress.org/Glossary