Importance: High

Type: User Experience

Schema are used by major search engines like Bing, Google, Yahoo! and Yandex to improve the display of search results, so that their user has an easier time finding the right Web pages.

Schemas are classified as types and under each type there are properties. A full listof schemas can be found at http://schema.org/

If you are a WordPress user, you might be interested in the Gensis Framework by StudioPress, which comes with schema and is SEO optimized.

http://my.studiopress.com/themes/genesis/