From schema.org:
This site provides a collection of schemas, i.e., html tags, that
webmasters can use to markup their pages in ways recognized by major
search providers. Search engines including Bing, Google and Yahoo!
rely on this markup to improve the display of search results, making
it easier for people to find the right web pages.
Many sites are generated from structured data, which is often stored
in databases. When this data is formatted into HTML, it becomes very
difficult to recover the original structured data. Many applications,
especially search engines, can benefit greatly from direct access to
this structured data. On-page markup enables search engines to
understand the information on web pages and provide richer search
results in order to make it easier for users to find relevant
information on the web. Markup can also enable new tools and
applications that make use of the structure.
A shared markup vocabulary makes easier for webmasters to decide on a
markup schema and get the maximum benefit for their efforts. So, in
the spirit of sitemaps.org, Bing, Google and Yahoo! have come together
to provide a shared collection of schemas that webmasters can use.
You should use the format specified at schema.org. Google, Microsoft, and Yahoo have all agreed to use the formats listed there.
