Semantic web and microformats

Page metadata is supposed to help search engines give useful information to users. Hence, it's something search engines are studying to use for web site indexing.

(schema.org) Article metadata .. Review metadata .. etc, they've defined on (schema.org) schema.org a whole bunch of schema's for web pages of various kinds. The (schema.org) documentation shows you how to get started.

(www.iacquire.com) 18 Meta Tags Every Webpage Should Have in 2013 Goes over Google Authorship, Facebook/OpenGraph metatags, Twitter Cards, and more.

(returnonnow.com) Semantic Markup: Adding Context To SEO (October 2013) This blog post goes over several essential semantic markups that can produce better search engine listings. Specifically it covers Authorship, Events, Videos, Products and Reviews, and more. Google in particular is looking for various markup items, and will produce different search engine results depending on what they find on the page.

(ogp.me) The Open Graph Protocol - The basis for Facebook metadata, Twitter Cards, and used by Google.